
Genus Pleonexes Bate
Stebbing, 1906: 642.
“Like Ampithoë, except that in peraeopods 3–5 the 6th joint is subchelately widened at the apex. Front lobes of lower lip bifid. Mandibular palp narrow, 3rd joint setose only at apex Peraeopods 1 and 2 have the 2nd joint rather broadly oval.”
There are 2 accepted species of this genus (excluding P. lessoniae), and 3 doubtful ones.
Pleonexes lessoniae n.sp. (Text-figs. 1, 2.)
Description of Male.
Length, 9 mm.; depth, 2 mm.; width, 2 mm. Eyes absent. Colour in spirit, white.

Text-fig. 1—Pleonexes lessoniae, n. sp. 1—Antenna 1, ♂ 2—Antenna 2, ♂. 3—Maxilliped. 4—Maxilla 1. 5—Maxilla 2. 6—Upper lip. 7—Lower lip. 8—Left mandible, male. 9—Right mandible, male 10—Left mandible, female 11—1st pleopod and epimeral plate 12—2nd pleopod and epimeral plate. 13—3rd pleopod and epimeral plate. 14—Coupling spine from pleopod peduncle 15—Uropod 1. 16—Uropod 2. 17—Uropod 3. 18—Uropod 3, dorsal margin of outer ramus 19—Telson, side view in male 20—Telson, dorsal view in female.

Antennae. First: Length, 3 ½ mm. Flagellum longer than peduncle, of 23 successively longer and narrower segments, each with pair of setae on superior angle, group of setae and 2 long flaccid sensory setae on inferior; accessory flagellum absent. Peduncle, 1st segment slightly longer and wider than 2nd; 3rd ½ length 2nd; a few surface setae, several on end margins. Second: Length, 3 mm. Flagellum shorter than peduncle, of 10 or 11 segments, the proximal 3 apparently in state of division; segments with 4 groups of setae on end margins, terminal segment tufted. Peduncle, 2nd segment small, gland-cone small; 5th segment 4 times and 4th 3 times length of 3rd, which is broader than long, has numerous setae on surface and inferior margin; 4th and 5th with groups of setae on margins and surface.
Mouthparts. Upper Lip: Distally setose; lateral margins medially notched. Lower Lip: Inner lobe almost as long as outer but much narrower, heart-shaped, distally bristled. Distal margin of outer lobe more or less horizontal; outer distal angle produced to short, sharp bristled lobe; inner distal angle to less obvious but more extensively bristled lobe; margin bristled between these lobes and outside outer angle. Outer proximal angle produced as largely inwardly and backwardly projecting curved mandibular process. First Maxilla: Outer plate the larger; the whole maxilla more like normal mandible. Outer plate narrows to end group of 10 strong, toothed spines; palp of 2 segments, 2nd segment twice length 1st, 3 or 4 end setae, palp not reaching as far as outer plate does. Inner plate small, subrectangular, barely reaching base of palp, single seta midway along inner margin. Second Maxilla: Inner plate the narrower, inner and end margins of both fringed with long plumose setae. Mandibles: Cutting edge, upper article a long incised plate, lower a small somewhat fan-shaped incised plate; molar process very weak, round and small, guarded proximally by 4 or so spines. Left mandible has spine row of 5 toothed spines, right has 6. Palp, 3rd segment missing, seems to arise on inner face rather than outer. Maxilliped: Palp 4-segmented. Inner plate subrectangular, reaching a little past merus base, strong spine on inner distal angle, long plumose setae on end and inner lateral margins. Outer plate ovate, reaches a little past propod base; inner margin has row of 14 setose stout teeth right to end; set back from them a row of about 5 medium-length setae, a few setae on inner margin proximally below teeth; distal ⅓ of outer margin has 9 medium-length plumose setae. Inner distal angles of basos and subrectangular ischium have 4 plumose spines. Merus proximally wide, sub-triangular, outer margin convex, 2 plumose setae on angle, inner margin sinuous. Carpus inner margin convex, with strong rows of plumose setae, twice length of own outer margin and as long as merus outer margin. Propod slightly narrower, margins convex, outer as long as merus outer margin. Inner and end margins of propod with long finely-combed spines; 2 or more on outer surface; group of plumose setae on propod outer distal angle. Curved dactylos has strong end nail; ½ propod length, surface has combs of minute bristles.
Gnathopods. First: Sideplate subrectangular, ventral angles rounded, a strong seta on posterodistal angle, short setae on ventral margin. Basos proximally constricted, width ⅓ length, single seta on anterodistal angle, convex posterior margin has about 6 long plumose setae medially Ischium narrower, as long as basos is wide, plumose setae on posterodistal angle. Merus subtriangular, posterior margin as long as ischium, with long plumose setae distally; anterior margin contiguous with proximal ⅓ of carpus posterior margin. Carpus subtriangular,

⅔ basos length, plumose setae on distal angles. Propod subrectangular, length more than 3 times width, longer than carpus, anterior margin has 4 groups of plumose setae; posterior has long single and grouped plumose setae. Palm transverse, ½ propod width, plumose setae either side, a single spine on one side at inner base of dactylos, a similar spine at end of palm on other. Dactylos longer than propod is wide, more than twice length of palm; inner margin has at least 9 sharp serrations, marked off distally by a strong seta; surface has row of many minute bristles. Second: (Left side) Subchelate. Sideplate trapezoid; a large seta at posterodistal angle, small setae ventrally. Basos proximally constricted, greatest width about ⅔ length; sinuous anterior margin has 6 or so single spines, convex posterior has about 5 long plumose setae medially. Ischium much narrower, subsquare, long setae on posterodistal angle. Merus as large as ischium, anterior margin contiguous with proximal ½ of carpus posterior margin; posterior margin convex, almost right-angled, row of long plumose setae with cup-shaped bases on distal ⅓, small combs of minute setae just above them. Carpus subtriangular, as wide as basos, as wide as long; anterior margin convex, distal ½ and anterior surface with many long plumose setae; posterior free margin lobed, lobe proximally has area of fine combs of minute setae; end and margins have long plumose setae which are so finely plumose that setae appear simple. Propod ovate; as long and as wide as basos; oblique sinuous palm defined by large stout spine at end; margins and surfaces have rows of long finely-plumose setae except for area down the middle. Posterior free margin of propod less than ½ length of anterior margin. Right gnathopod: Palm much shorter, concave, with distinct sharp angle, defined by angle and spine. Dactylos over-reaches palm, which is ½ propod width, inner margin has large strong serrations forming teeth.
Peraeopods. First: Sideplate ovate, ventral margin rounding to anterior, small setae ventrally, posterior margin straight. Basos almost oval, greatest width about ⅔ length; posterior margin has 3 or 4 long setae ½ along; a few minute setae on angle. Ischium subrectangular, posterior margin as long as merus and ¼ basos length; merus as wide distally as long, anterior margin slightly convex, anterodistal angle produced in narrow process ½ along carpus with 4 or so setae terminally; posterior margin has setae distally. Carpus slightly shorter and narrower than merus, 1 or 2 small setae anterodistally, posterior margin has long setae. Propod ⅓ basos length, tapering to dactylos; long setae medially and distally on anterior margin and distal ⅔ of posterior. Stout curved dactylos ⅔ propod length. Second: Similar, shorter. Third: Sideplate, ovate anterior lobe has convex ventral margin; ovate posterior lobe extremely small. Basos ovate, almost circular, 1 or 2 setae on anterior margin, short single setae around posterior; distal posterior surface almost reaches merus. Ischium small, 2 or 3 setae on anterodistal angle. Merus nearly twice ischium width, width ½ length; proximally constricted, posterodistal angle produced bluntly downwards a little, setae on margins. Ovate carpus not quite merus length, much narrower, width ½ length, 1 or two setae ½ along each margin, several on angles. Propod subchelate, as long as merus, widening distally to form palm, distal width nearly ½ length, 2 or 3 groups of setae on margins. Palm less than ½ propod width, anterodistal angle with spine, produced a little distally; several long setae immediately below palm; strong curved finger much longer than propod is wide, greatly overlapping palm. Fourth: Basos anterior margin concave, posterior margin straight, narrowing distally; greatest width ⅔ length; posteroproximal angle bluntly rounded

Text-fig. 2.—Pleonexes lessoniae, n.sp. 1—Gnathopod 1, male. 2—Gnathopod 1, female, propod. 3—Gnathopod 2, male, right propod 4—Gnathopod 2, male, left gnathopod. 5—Gnathopod 2, female, last 4 segments. 6—Peraeopod 1, male. 7—Peraeopod 2, male. 8—Peraeopod 3, male. 9—Peraeopod 4, male. 10—Peraeopod 5, male.

and produced slightly upwards; a few small setae on margins, spine on posterodistal angle. All segments much longer in proportion to width than Pr. 3; otherwise similar. Fifth: Longer than Pr. 4; basos and other segments proportionately narrower; otherwise similar.
Epimeral Plates. Ovate, small. First and second almost semicircular.
Pleopods: Inner ramus slightly the longer, rami longer than peduncle, of about 16 plumosely-setose segments; 2 arrow-headed coupling spines on peduncle, 1 to 6 plumose spines on each margin.
Uropods. First: Rami subequal, ½ peduncle length. Peduncle outer dorsal margin has 3 to 6 short strong seta-tipped spines distally; broken row of setae along inner margin proximally; spine on ventrodistal angle. Outer ramus widest medially, 4 or 5 seta-tipped spines dorsally, 3 short spines and 1 long one on end; ramus margins convex; inner ramus dorsally naked, about ½ width of outer, upper margin concave, 1 long and 2 short spines at end. Second: As long as 1st; in situ reaching past 1st and 3rd. Peduncle stout, over twice length outer ramus; 8 or 9 seta-tipped spines dorsally; produced in small lobe superodistally. Outer ramus the longer, 4 or 5 seta-tipped spines dorsally, 1 long and 3 short spines at end; margins convex so ramus widens proximally, narrows distally; dorsal and end margins minutely toothed most of length. Inner ramus ½ width of outer, upper margin concave; 1 short, 1 long spine and a seta at end. Third: Inner ramus more than ½ length outer; both much less than ½ peduncle length. Peduncle broad, dorsal margin has 3 or 4 groups of long sparsely-plumose setae; ventral margin convex proximally, 2 or 3 plumose setae at ventrodistal angle; series of fairly long plumose setae on inner distal margin along base of inner ramus. Inner ramus sub-circular, about 9 plumose setae distally; outer ramus, ventral margin convex, 2 large uncinate spines terminally, dorsal margin straight with about 9 curved strong conical teeth, these the most prominent of combs of similar teeth on either side of margin and extending to end, those furthest from dorsal margin the smallest. Telson: Two large uncinate spines at end; telson in side view ovate, almost spherical; 2 small setae dorsal to, and at base of, spines; in dorsal view telson subtriangular, narrowing to the terminal spines which give telson anchor-like appearance when flattened by mounting; slightly notched between spines.
Description of Female.
Length, 5 ¾ mm.; depth, 1 ¾ mm.; width, 1 ¾ mm.; carrying at least 9 ova.
Antennae. First: The longer, about 15 segments, length, 3 ¾ mm. Second: Reaching ⅔ along flagellum of 1st; length, 3 mm.
Gnathopods. First: As in male, carpus a little broader comparatively. Second: Sideplate, anterior margin rounding more broadly to ventral than in male and destroying quadrate appearance; posterior slightly concave. Carpus and propod differ slightly from male, most noticeably in lack of profuse setation on anterior margins, there being only a distal tuft on carpus and about 5 rows of up to about 6 setae on propod. Carpus about ½ propod length; palm oblique, straight, defined by spines, like that of right gnathopod of male more than left.
Locality. Island Bay, Wellington, on Lessonia variegata, coll. J. G. Gibbs, ⅛/50.*
Type Slides 90, male; 91, female. Personal collection.
[Footnote] * I have since recorded this species from Otago Harbour —D E. H.
