282 THE VOYAGE OF H.M.S. CHALLENGER. 



beyond the dorsal line, and situated rather in front of the centre of it. The hinge-line is 

 slender and finely dentate nearl}' from end to end, some of the denticles near the middle 

 being the smallest, and a few at the posterior extremity the largest. The interior is 

 glossy, but hardly jjcarly, the muscular scars Ijeing indistinct. 



Length 5^ mm., height 2^, diameter 2. 



Hahitat. — Station 24, off Culebra Island, West Indies, in 390 fathoms ; Pteropod ooze. 



This curious species is not " nacreous " like the type of the genus Idas, and of a very 

 different form. I cannot discover in any of the odd valves (no complete specimen was 

 obtained) any trace either of an internal or external ligament. It is, I expect, of a very 

 slight character, and marginal. 



. ' Dacrt/diam, Torell. 



Dcccrydiiim vitreum (MciUer). 



MoiUola (?) vitrea, MiJller, Ind. !iroll. Gronl., p. 19. 



Dacrijdium vitreurn, Torell, Spitzbergens Molluskeufauna, p. 138, pi. L tigs. 2, a, h. 



Dacrydiuin vitreurn, Jeffreys, Ann. and Mag. Nat. Hist., 1876, vol. xviii. p. 429. 



Dacrydium vitreurn, Jeffreys, Proc. Zool. Soc. Lond., 1879, p. 569. 



Dacrydium vitreurn, Sars, Moll. Eeg. Arct. Norv., p. 28, pi. iii. figs. 2, a, h. 



Hahitat. — Stations 73 and 78, west and east of the Azores, in 1000 fathoms. 



For the synonymy and distribution of this species reference .should be made to the 

 above quoted j)apers by the late Dr. Gwyn Jeffreys. 



Dacrydium occidental e, n. sp. (PI. XVII. figs. 1-la). 



Testa Dacrydio vitreo similis, sed magis quadrata, margine inferiori magis incur- 

 vato, dorsali minus convexo. 



This species resembles Dacrydium vitreurn in colour, texture, sculpture, and hinge, 

 but appears to be constant in its difference of form. It is not quite so convex, has a less 

 peaked anterior end and a more oblong-squarish appearance, the margin Ijehind the 

 umbones being less sloping backwards, the arcuation at the middle less prominent, and 

 the ventral outline more concave. 



Length 4^ mm., height 2f, diameter if. 



Hahitat. — Station 24, off Culebra Island, West Indies, in 390 fathoms ; Pteropod ooze. 



Hacrydium meridionalis, n. sp. (PI. XYII. figs. 2-2o). 



Testa tenuis, alba, ixregulariter subpyriformis, mediocriter inflata, liris tenuibus con- 

 centricis aliisque paucis radiantibus cancellata, striis incremeuti sculjjta. Umbones parvi, 

 ad apicem obtusi, peculiariter clypeati. Margo cardinalis mediocriter elongatus, rectus, 

 inferior late rotundatus. Latus anticum leviter incurvatum, posticum excurvatum. 



