222 



inent rounded edge, is marked with numerous very close- 

 set vertical striae, and does not extend so far in front as 

 behind, where it gradually narrows and vanishes. It is 

 divided by a rather wide, shallow, subcentral triangular carti- 

 lage-pit. There, are four anterior teeth perpendicular to the 

 margin, and four posterior convexly curved towards the 

 umbo ; three or four small marginal teeth inside the anterior 

 end, four at the post-dorsal margin, and three or four obso- 

 lete teeth at the post-ventral border. Margin otherwise 

 simple. Posterior muscle-scar long, large, triangular. Crowd- 

 ed concentric, rather irregular accremental striae, with very 

 fine broken radial incisions. 



Dimensions. — Antero-posterior, 2'4 mm. ; umbo-ventral, 

 2 mm. 



Locality. — MacDonnell Bay and Guichen Bay, in shell- 

 sand. 



Variations. — When dead they become white, the amber 

 colour disappearing first about the umbo, and last about the 

 ventral margin. Some show four obscure rounded radial 

 ridges, from the umbo to the posterior inferior angle : and 

 these may crenulate the margin. Dorsally to these the shell 

 may be somewhat hollowed. The posterior marginal teeth 

 may crenulate the border, as may also the front teeth. 



Bathyarca perversidens, Hedley. 



Bathyarca perversidens, Hedley, Memoirs of Australian Mus., 

 1902, vol. iv., part 5, p. 298, fig! 45. Type locality, off Port 

 Kembla, in 63-75 fathoms, etc. Var. — Bathyarca cyhcea, Hed- 

 ley, Trans. New Zealand Inst., 1906, vol. xxxviii., 1905, p. 70, 

 pi. 1, figs. 3-4. Type locality, 110 fathoms, east of Great Barrier 

 Island, New Zealand. 



Dredged off Cape Jaifa, in 130 fathoms, 2 valves; in 

 300 fathoms, very many valves. 



A series was submitted to Mr. Hedley as B. cybo'a, and 

 he kindly compared with his types and confirmed the identi- 

 fication. A suggestion was also put forward that his two 

 shells were variants of one species, and he allowed that my 

 series seemed to bridge the interval between the two. Being 

 persuaded they are conspecific, I have named them B. per- 

 versidens, which has priority, making B. cyhcea a variant. 



In all my specimens the right valves have much more 

 pronounced sculpture than the left, especially the radial. 

 Some shells have the sinuation at the gape quite deep, with 

 the depression from this to the umbo marked, others but 

 slight, and others not at all. Some have quite a distinct 

 angle at middle of the posterior side, where a straight-dor- 

 sal half meets the rounded ventral part ; in others the pos- 

 terior side is continuously curved. 



