Genus Cytherideis, Jones.
Cytherideis hedleyi, sp. nov.
Plate III, 8 a-c.
Description—Carapace elongated, compressed. Seen from the side, arcuate and siliquose; depressed in front; greatest height about the middle; posterior extremity slightly produced at the ventral angle; back evenly arched, ventral edge sinuous. Edge view elongate-ovate, rounded at the back, compressed in front; greatest thickness about the middle of the lower third. Surface of carapace ornamented with closely set polygonal areolæ or pittings, arranged in more or less regular concentric lines. A linear series of muscle-spots situated in a lateral depression of the carapace just below the median area. Length, 0 6mm.; height, 0·225mm.; greatest thickness of carapace, about 0·66mm.
Affinities.—In outline our species is somewhat comparable with C foveolata, G. S. Brady,* with the exception that the valves of that species are not produced in the postero-ventral region; it further essentially differs from ours in the surface-markings of the carapace, which in C foveolata consist of a minute and dense punctation.
Another form of the same genus which we may compare with the present species is C ondrewsi, Chapman,† which, however, shows the following differences: Test less depressed at the anterior end; ornament not so distinctly polygonally areolate, and muscle-spots arranged in rosette form.
Very rare in our sounding.
[Footnote] * Ann. Mag. Nat. Hist., ser. 4, vol. vi, 1870, p. 454, pl. xix, 1–3.
[Footnote] † Proc. Zool, Soc. Lond., 1902, p. 229, text 27.