786 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XX. 



rounded, obtuse, often prominent lines of growth with a thin yellowish 

 brown epidermis which, under the lens, is closely covered with minute 

 granules often arranged in more or less distinct concentric lines. The 

 posterior hinge-margin is somewhat thickened, the ligamental groove 

 is long and curved, diverging considerably from the margin of the 

 shell at its posterior end and extending forward under the beak. Mus- 

 cular scars a.nd pallial line in the largest specimens strongly marked ; the 

 anterior scar is considerably elongated and has a number of lobes or 

 scallops on its inner margin. 



Length of a medium-sized specimen, 27 mm.; height from siphonal 

 lobe to beak, 27 mm. ; breadth, 14 mm. Length of a larger, more ovate 

 specimen, 32 mm. ; height from siphonal lobe to beak, 35 mm. ; breadth, 

 21 mm. 



This species presents considerable variation in outline and in the 

 degree of convexity of the valves; some are subquadrate in form, 

 others subcordate, and others pretty well rounded, but the majority 

 are oblong-obvate with a posterior truncation, corresponding to the 

 broad radial groove; some of the valves are considerably inflated, but 

 most of them are more compressed than is usual in this genus. There 

 is also considerable variation in the prominence of the siphonal lobe 

 and broad .radial ridge, and in the size of the lines of growth, which in 

 some specimens are quite fine and regular, and in others unevenly 

 developed, those on the anterior part appearing almost like concentric 

 ribs. 



Many separate valves, at four stations between IS", lat. 44 54', W. ; 

 long. 59 46' 45", and 2*. lat. 42 19', W. long. 69 47', in 65 to 471 

 fathoms, 1879 and 1885. 



The single valve found off Cape Cod, 1879, and identified as Cryp- 

 todon sarsii, proves to be the young of this species. 



CRYPTODON PLICATUS Verrill. 



(Plate LXXXIX, fig. 6.) 

 Cryptodon plicatns VERRILL, Trans. Conn. Acad., VI, pp. 437, 450, 1885. 



One young live specimen and one imperfect valve of this character- 

 istic and fragile species were found at two stations, off Marthas Vine- 

 yard, in 1,073 to 1,122 fathoms, 1884. 



CRYPTODON CROULINENSIS (Jeffreys) Smith. 



(Plate XC, figs. 3, 4.) 



Clansina croulinensis JEFFREYS, Ann. Mag. Nat. Hist., XX, p. 19, 1847. 



Axinus croulinensis JEFFREYS, Brit. Con., II, p. 250, 1864. G. O. SARS, Mollusoa 



Eeg. Arcticae Norvegise, p. 62, pi. 19, figs. 8, a-b, 1878. JEFFREYS, Proc. Zool. 



Soc., London, p. 703, June, 1881. 

 Cryptodon croulinensis SMITH, E. A., Eeport Voy. Challenger, Zool. Larnelli- 



branchiata, XIII, p. 193, 1885. 



Shell small, obliquely subovate, with the beaks prominent, and the 

 anterior end considerably the longer. The antero-dorsal margin is 



