REPORT ON THE LAMELLIBRANCHTATA. 195 



Cryptodon sp. 



Habitat. — Station 23, off Sombrero Island, West Indies, in 450 fathoms. 



A single right valve of a small species was dredged at this locality, which appears 

 to be distinct from any j^reviously described. It is somewhat like Cryptodon croulin- 

 ensis in size and form, but does not exhibit any depression down the posterior side. 



Family Ungulinid^. 



Diplodonta, Bronn. 

 Diplodonta subgranulosa , n. sp. (PI. XIV. figs. 7-7a). 



Testa subinflata, insequilateralis, alba, antice angustata, acute rotundata, postice longe 

 latior, concentrice leviter striata, ubique minute rugosa vel subgranulata. Umbones 

 parvi, acuti, leviter involuti. Margo dorsi posticus subhorizontalis, rectiusculus, anticus 

 valde obliquus, levissime curvatus. Margo ventris arcuatus, antice multum adscendens. 

 Margo dorsalis antice breviter, baud profundeque intus sulcatus. Dens cardinis duplex 

 valvse sinistrse infra umbonem situs, profunde fissus, valde erectus ; dens posticus tenuis, 

 lamellaris, obliquissimus. Ligamenti fossa intra marginem locata. 



This species is rather convex, considerably inequilateral, much narrower in front than 

 behind, white, not glossy, exhibiting fine concentric lines of growth, and sculptured 

 throughout with a very fine subgranulation. The dorsal outline is scarcely curved on 

 either side, the hinder portion being horizontal and the anterior part very oblique. The 

 front extremity is sharply rounded, whilst the opposite side is much more broadly 

 curved, forming at the upper part an obtusely rounded shoulder. The umbones are 

 small, but very little raised above the hinge-line, acute, somewhat incurved and directed 

 forwards. The hinge-plate beneath the beaks is broadish, so that the teeth do not pro- 

 ject beyond it. The double one in the left valve is thick, prominent, triangular, deeply 

 cleft at the top, and falls perpendicularly immediately beneath the apex of the beak. The 

 posterior tooth is very slender and oblique, and the ligamental groove is within the 

 outer margin, so that scarcely any portion of the ligament itself would be visible 

 exteriorly. Besides this groove the hinder margin exhibits only the faintest furrow, but 

 the anterior side is more distinctly sulcate, the groove, however, being short and 

 shallow. 



Length 5f mm., height 4f, diameter 3^. 



Habitat. — Station 208, Philippine Islands, in 18 fathoms ; blue mud. 



The form and the surface, which has a minutely shagreened appearance, are the 

 characteristics of this species. 



