154 AMERICAN JOURNAL 



by me in Norton Sound ; Leda, apparently ventrieosa, Hinds, 

 from the mouth of a sole, Bay of Yeddo, Japan ; and a Yoldia, 

 apparently electa, A. Ad., from the head of the Gulf of Califor- 

 nia, by Dr. Palmer. With the latter were valves of a very small 

 undetermined species of Nucula. Nucula expansa, Rve., oc- 

 curred from Bering Strait to Sitka, in five to thirty fathoms. 



MYTILIDiE. 



MODIOLARIA DENTICULATA, n. S. 



Shell with a thick blackish brown epidermis, furnished poste- 

 riorly with strong, fine, projecting beards, which entangle parti- 

 cles of sand, &c, and form a solid mass of regular form, which 

 cannot be removed without crushing the shell. There is an ob- 

 tusely rounded carina to the posterior end of the shell, and by 

 the formation alluded to this carina is greatly exaggerated, 

 sharpened, and made to terminate in a sharp point some distance 

 beyond the end of the shell. The general form of the valve 

 itself is elongate-ovate, with a not prominent umbone. Both 

 ends of the margin are gently rounded, the anterior end being 

 slightly the smaller. There is a slight gape and concavity in the 

 middle of the ventral margin, otherwise both dorsal and ventral 

 margins are nearly equally arched. The entire margin is denti- 

 culate, and the denticles are especially strong on the hinge mar- 

 gin, which is interrupted for the large and strong ligament. The 

 beaks are deep and vaulted, and the valves inflated. 



The color of the shell is pearly white, with a purple spot be- 

 hind the posterior muscular impression, and the umbones tinged 

 with purple. The epidermis is blackish brown, thick, and liable 

 to peel off"; it is marked with faint radiating lines, as nearly as 

 the incrustation will admit of perceiving. 



Lon. *7, alt. *4, diam. *4 in. 



Habitat, Acapulco, Mexico, Dall, 1868. 



This very curious species is unlike any other which I know of. 

 In some respects it is approached by Modiola opifex, Say, which 

 is a much more elongated shell, from Rio Janeiro, Brazil. 



Modiola aterrima, n. s. 



Shell small, subtriangular, black. Umbones nearly terminal. 

 Exterior smooth, covered with a polished epidermis, marked only 

 by lines of growth ; usually somewhat eroded. Ligamental cal- 

 lus white, narrow. Dorsal margin angulated more or less at the 

 end of the ligament behind. Posterior end broadly rounded. 

 Anterior end narrow, bluntly rounded. Hinge line without 



