144 W. B. Dwight — Recent Explorations in the 



black flattened cone. In one specimen, the shell shows consid- 

 erable thickness. The one figured is the best one found, 

 though it is the internal cast, the shell being entirely exfoliated. 

 The shape is an acute cone very slightly convex on the visible 

 surface, and with a few evident annulations in the upper half, 

 the most marked one being next to the aperture. The shape 

 of the transverse section is unknown, though it has been 

 sought for by making cross-sections. 



A single operculum has been found, but it is not sufficiently 

 perfect to warrant its description. This fossil may be most 

 safely referred to H. Billingsi. Specimens of the above 

 named species, kindly loaned to me for examination by Mr. 

 C. D. Walcott, show distinctly the annulations which appear in 

 the Stissing fossils. 



Z,eperditia ebenina, n. sp. Plate VI, figs. 2, 3 and 4. 



Carapace jet-black, shining, subelliptical ; about eight milli- 

 meters long, and five millimeters high in the largest specimens 

 collected. [Dorsal margin straight, or nearly so, somewhat 

 shorter than the longest diameter of the carapace. Ventral 

 margin arcuate ; terminal margins well-rounded ventrally, but 

 above sloping inward, in straight lines, to the dorsal margin ; 

 dorsal angles somewhat obtuse, not at all rounded. 



The carapace in general is quite convex ; in the largest 

 specimens, as in one of those here figured (fig. 3), there is a 

 broad and rather flat depression passing centrally from the 

 dorsal to the ventral edge, leaving two terminal prominences ; 

 but as in such cases cracks are evident in the shell, and as the 

 smaller specimens do not exhibit this feature, it is probably the 

 result of compression. On account of the imperfection of the 

 specimens, and the frequent distortion by pressure, it is not at 

 present possible to determine the normal outlines of surface 

 convexity. 



The external surface of the carapace is very peculiarly orna- 

 mented. The entire border of each valve, in the form of a 

 strip which is nearly two millimeters wide in the largest speci- 

 mens, is covered with extremely minute contiguous pits. 

 There are at least from 100 to 150 to a square millimeter. 

 Within this finely-pitted border, the entire central portion is 

 covered with much larger, separated pits, the interspaces being 

 as wide as the pits themselves, or wider. Their disposition is 

 very irregular, but they average about 15 or 20 to the square 

 millimeter. There is a linear marginal groove extending along 

 the ventral border ; at its central point it is nearly one milli- 

 meter within the ventral margin, but it gradually approaches 

 it toward each extremity until it coalesces with the terminal 

 margins. The central portions of the internal surface of the 



