788 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XX. 



4.5mm.; height, 5.25 mm. In this the anterior or upper plication is 

 much less distinct than in the type, and it is therefore possible that 

 this feature is abnormal. 



CRYPTODON EQUALIS, new species. 

 (Plato XCI, figs. 5, 6.) 



Shell of moderate size, grayish white, rather swollen, pyriform, usu- 

 ally a little higher than long, but sometimes the height and length are 

 about equal. Umbos rather prominent; beaks median, conspicuously 

 raised above tbe margin and curved strongly forward so as to produce 

 a rather deep, broad, cordate, but ill denned lunular area. Anterior 

 and posterior ends nearly equal. The dorsal margin slopes rapidly on 

 both sides of the beak; anteriorly, in the lunular region, it is nearly 

 straight; the anterior end is pretty evenly rounded, forming a continu- 

 ous curve with the ventral margin, which forms nearly a semicircular 

 curve; the posterior end has one broad, shallow undulation which 

 causes a slight incurvature in the postero-ventral margin ; above this 

 the dorsal margin is very slightly convex and forms an angle at the 

 commencement of the fold. The ligameutal area is marked by a smooth, 

 long, lanceolate, slightly sunken portion, clearly separated by an 

 incised line. The general surface is covered with slightly marked, 

 more or less irregular lines of growth. The hinge-margin is moderately 

 thickened and is essentially the same in both valves. There is a well 

 marked swelling both before and behind the beak and a more con- 

 spicuous one immediately under it; a less conspicuous thickening, with 

 its external edge excurved, extends along the postero-dorsal margin, 

 in the ligamental region. Muscular and pallial scars indistinct. 



Length, 5 mm.; height, 5 mm.; thickness, 4 mm. Some specimens 

 are somewhat larger than this. 



In the large series which we have of this species there is some 

 variation. In some cases the form is less swollen, the length is 

 slightly in excess of the height, so that the general outline is more 

 evenly rounded. The species is, however, notable for the equality of 

 the anterior and posterior ends and the presence of the single slight 

 undulation. Cryptodon t/otildii somewhat resembles this species, but 

 differs in being longer in proportion to its height, in its more com- 

 pressed form, and in having two distinct folds or undulations. It is 

 also closely allied to C.flexuosus of Europe, but is more pyriform in 

 shape and lacks the anterior angulatiou noticeable in that species. 



Taken at thirty-two stations, between N. lat. 47 40', W. long. 47 35' 

 30", and N. lat. 37 OS', W. ioug. 74 33', in 94 to 1,537 fathoms, 1873- 

 1886. 



CRYPTODON PLANUS, new species. 

 (Plate LXXXVIII, figs. 3, 4.) 



Shell small, well-rounded, the length and height about equal, with 

 the beak small, prominent, nearly central, curved strongly forward, 





