LEPIDOPLEURUS. 7 



ginatus, and without the dingy blackish painting of either. L. can- 

 cellatus is narrower, higher, and with a sharper median angle. In 

 L.faliginatus the middle valves are shorter from front to back, the 

 sutural laminae smaller and much more triangular. There is no 

 sign of a mucro on these valves, but in L. pergranatus there is a 

 beginning of one, quite perceptible. The latter is a proportionally 

 wider and flatter species, with a stronger and more prominent girdle 

 densely set with elongated silvery scales like short stiff gray hairs; 

 these form a pretty fringe at the periphery. The sculpture follows 

 the pattern of L. cancellatus, but the lateral areas are less clearly 

 defined, the granules are more clearly cut, more regularly arranged 

 and larger than in any of the species hitherto known. There are 

 twelve gills on each side, reaching forward to about the middle of 

 the sixth valve. (Dall.) 



L. BELKNAPI Ball. PI. 1, figs. 18-22. 



Shell elongated, much elevated, dorsally angled ; whitish, more 

 or less tinged with ashen or black. Valves elevated, with distinct 

 apices ; mucro central, conspicuous. Sculpture as in L. alveolus, 

 but the granules of the dorsal areas sparse, and disposed in quin- 

 cunx. Posterior valve concave below the apex, sinuated behind. 

 Girdle narrow, having delicate spicules toward the margin. (DalL} 



Length 10, breadth 3 mill. ; divergence 90. 



North Pacific Ocean in lat. 53 08' N., Ion. 17 19' W., at a depth 

 of 1006 fras. ; off Cape Bolinas, Luzon, Philippines, 1050 fins. 



Leptochiton belknapi DALL, Proc. IT. S. Nat. Mus. 1878, p. 1, 

 Jan., 1878 ; L c. p. 317. HADDON, Challenger Rep. xv, p. 10, t. 1, 

 f. 2 ; t. 2, f. 2. 



This specimen much resembles L. alveolus, to which I at first 

 referred it. A careful microscopical examination, however, shows 

 differences which I am disposed to consider specific ; but I have 

 but one specimen, and others might show modifications in these 

 particulars. The differential characters are as follows : In alveolus 

 the pustules are distributed evenly, closely and in no pattern what- 

 ever, all over the surface. In belknapi, they are more widely 

 separated and arranged in quincunx on the dorsum, the spaces 

 seeming to radiate from the median dorsal line. In alveolus the lat- 

 eral areas are barely perceptible. In belknapi they are raised, con- 

 centrically rugose, and the pattern of the pustular arrangement is 

 different and more irregular than that on the dorsum. In belknapi 



