4 EDGAR A. SMITH. 
Although the general aspect of this species is very unlike that of the type of 
the genus Cyamium, still the characters of the hinge appear to be so very similar 
that it does not seem to be advisable at present to separate them generically. 
DIPLODONTA INCERTA. 
(Pl. IIL, figs. 5, 5a.) 
Shell very inequilateral, small, thin, whitish, moderately convex, sculptured with 
fine lines of growth, and exhibiting a radiating ridge or rounded angle from the 
umbo to the lower posterior extremity ; umbo antemedian, consisting of a distinctly 
marked, smooth, pellucid, convex, rounded embryonic disc; anterior dorsal margin 
much descending ; posterior curved, horizontal, posterior end terminating below in a 
point at the end of the radiating ridge; anterior end sharply curved ; lower margin 
gently arcuate; interior smooth, glossy, exhibiting a groove beneath the exterior 
radiating angle, and some shallow sulcations corresponding with the more distinctly 
marked lines of growth of the exterior; two divergent cardinal teeth in the right 
valve (fig. 5a, 1), the anterior one being just in front of the apex of the umbo, 
and the posterior immediately beneath it; ligament internal (fig. 5a, 2), in a narrow 
furrow behind the hinder tooth ; scars and pallial line indistinct. 
Length, 6°75 millim. ; height, 5°5; diam., 5. 
Winter Quarters, 130 fathoms. 
One right valve only. Provisionally placed in Diplodonta, although the ligament 
is rather more wholly internal than in that genus. 
PHILOBRYA LIMOIDES. 
(Pl. IIL. figs. 2-2b.) 
Shell small, equilateral, moderately convex, thin, dirty whitish, clothed with a 
deciduous, fibrous periostracum, sculptured with concentric lines of growth and some 
raised, slender, radiating, threadlike lines, from which spring short, epidermal hairs or 
fibres of a darker colour than the rest of the epidermis; umbones obtuse at the 
apex, which consists of a distinct protoconch, radiately lirate, minutely concentrically 
striated, and having a straight hinge-line ; the dorsal margins of the adult shell are 
very sloping, nearly rectilinear, the posterior grooved to hold the ligament (figs. 2b, 1), 
and the anterior terminating just in front of the umbones of both valves in a 
small, shelly projection ; lateral and ventral margins more or less distinctly denticulate 
within and slightly thickened; interior of valves dirty whitish, smooth, exhibiting a 
large but shallow posterior adductor scar in the form of a 6; anterior scar not 
traceable, perhaps absent. 
Length, 8 millim.; height, 9°5; diam., 4°5. 
Winter Quarters, 20-130 fathoms. 
Remarkable on account of the peculiar protoconch, the epidermis, and the 
