4 EDGAK 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. 



DlPLODONTA INCERTA. 



(PI. III., 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, l), 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. 

 (PI. III., 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, l), 

 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, 20-1 30 fathoms. 



Eemarkable on account of the peculiar protoconch, the epidermis, and the 



