Art. XVII.—On a new Genus of Rissoinæ.
[Read before the Philosophical Institute of Canterbury, 3rd November, 1881.]
There is a small mollusc, common in the rock pools in Lyttelton Harbour, that I cannot bring into any genus in Adams' “Genera of Recent Mollusca.” The shell is like that of Barleeia, but the operculum is sub-spiral, like that of Rissoina, but without the marginal ridge. The animal differs from Rissoina in having the opercular lobe simple, and the foot emarginate behind, as in Barleeia, but from this genus it differs in having the tentacles long and setaceous, and the rostrum emarginate. From all other genera it is distinguished by the process on the operculum.
Dardania. Gen. nov.
Animal. Foot large, rounded in front, and emarginate behind; opercular lobe small, simple. Rostrum emarginate at the extremity; tentacles long, and setaceous; eyes large, on swellings at the outer bases of the tentacles. Operculum ovate, sub-spiral, with a long shelly process from below the nucleus. Shell ovate, sub-conical; whorls smooth; aperture oval, entire, rounded in front, peritreme not continuous, outer lip thin; axis imperforate.
D. Olivacea. Sp. nov.
Plate I., fig. K.
Shell small, ovate, olive brown when alive, purplish black when dry; whorls four, convex, smooth, with fine lines of growth. Length .08: breadth .06.
Animal light brown, foot and tentacles white. The sole of the foot has a median longitudinal groove, and the tentacles are smooth. The central tooth is as broad as long, and with two denticles on each side of the median denticle. The first lateral tooth has five denticles, the middle one larger than the others. The second lateral has three denticles, the inner one the smallest. The third lateral is narrow, abruptly bent and expanded near the base, it has three minute denticles.
Habitat: On seaweed in rock pools; Lyttelton Harbour.
It is probable that some of the New Zealand species described as Rissoina, or Barleeia, may belong to this genus, as in none of them is the animal or the operculum known.
Explanation Of Plate I., fig. K.
K Dardania olivacea, × 10 times.
" animal × 10 times.
" teeth × 470 times.
" operculum, inside, × 30 times.