BIVALVIA. 119 



18. Nucula sphenoides, Edwards, MS. Tab. XVIII, fig. 2, and Tab. XIX, fig. 2 a, b. 



Spec. Char. N. testa minutd, irregulatim trigond vel sphenoided, tumidd, lavissiu/d, 

 politd ; pedi-regione ovato-angulatd ; siphoni-regione brevissimd, truncal d ; ano distinclo, 

 circumdato, in medio prominenti ; lunula elongatd, depressd, divisd ; margine dorsali sub- 

 arcuatd ; margine ventrali convex a ; marginibus crenulatis. 



Shell small, roundedly triangular or wedge-shaped, tumid, smooth, and glossy ; pedal 

 region obtusely pointed ; siphonal region very short, with a prominent anal corselet 

 surrounded by a depression ; ventral margin very convex, with the edges crenulated. 



Length, ^ths of an inch. 



Localities. Hempstead, Brook? {Edwards). 



A few specimens of an elegant little species enrich the cabinet of Mr. Edwards, and 

 there is attached to them the above name in MS. They very closely resemble a species in 

 the Paris Basin figured and described by M. Deshayes under the name of N. Greppini, 

 especially the specimen represented by fig. 2, Tab. XIX, and when the specimens them- 

 selves are compared they may possibly prove to belong to the same species, but I have 

 not the means of doing this. There is, however, an apparent difference, which I may here 

 point out. Our shell has the dorsal margin less curved, while the ventral margin is more 

 so, than is represented in the figure of N. Greppini, Desh., p. 882, pi. Ixiv, figs. 13 — 10 ; 

 and it has a distinct lunule or dorsal depression, divided by a slight central ridge, and 

 it is more tumid. The anal region also has apparently a more prominent centre and 

 deeper external depression. 



19. Nucula sericba, S. Wood. Tab. XIX, fig. 3. 



Spec. Char. N. testa lenui, transversa, subtrigonuld, Icevigatd, glabra, calvatd aut 

 obsolete radiatd ; pedi-regione productd, angulatd ; siphoni-regione oblique truncatd, sub- 

 altenuatd ; lunula inconspicud ; margine dorsali convexiusculd ; margine ventrali arcuald ; 

 umbonibus acutis, terminalibus ; marginibus crenulatis. 



Shell thin, transverse, subtrigonular, smooth, glossy, naked, or with obsolete radiating 

 striae ; pedal region produced and angulated ; siphonal side obliquely truncated, and 

 somewhat pointed ; lunule inconspicuous ; dorsal margin slightly convex, ventral margin 

 more curved ; beaks terminal ; inner margins crenulated. 



Length, \ an inch. 



Localities. White Cliff, Hunting Bridge (Ldivards). 



This species somewhat resembles pralongata and protracta, but it protrudes more on 

 the siphonal side, and the ventral margin is more rounded. It differs also in the anal 



