238 CEETACEOUS PELECYPODA 



Types, E. migulosa^ d'Orb., or R. Mortonl, Mant. In the first the internal 

 ridges of the attached valve do not seem to be present, in the latter they are well 

 developed, bnt do not reach to the margin. Bayle and others have referred this 

 last species to SphmnilUes, but this is, I believe, a mistake. I also think that 

 several other species, as Rad, Failetteana and Martiniana of d'Orbigny, rather 

 belong to this genus than to Sphcerulites^ to which they had been referred by 

 Bayle. 



2. *S^/^<^r^«Z^Y6'5, de la Merth., 1805, (Bayle, ibid., p. 800). Attached valve 

 generally elongately conical with longitudinal more or less foliated surface and 

 the margins radiately ribbed, internally with a single umbonal rib extending the 

 whole length of the valve. Eree valve smaller, similar in form and structure to 

 that of Radiolites, but with a median tooth or columella corresponding to the hinge- 

 rib of the other valve, in which there is on each side of the rib a cartilage -process, 

 the two cartilage-plates being sometimes united in front, and next to them are 

 situated the raised muscular scars. Type, SphcBrulites angeiodes, Picot de la Peir. 



The presence of a hinge-rib readily distinguishes the present genus from the 

 former, and the absence of any other ribs or folds in the attached valve separate 

 it from Hippurites. In several tolerably well preserved specimens of the lower 

 valve I have not been able to trace the extent of the muscular impressions, but 

 from some valves figured by d'Orbigny they seem to be very large. In the 

 upper valves I have seen no special hinge-teeth or lamellae, but whether they do 

 not exist in some species, as has been recorded, I am unable to say. 



3. Hippurites, Lamck., 1801. Lower valve large, more or less distinctly 

 conical, attached at the end, generally longitudinally sulcated on the surface, base 

 internally chambered ; hinge consisting of a single hinge-rib or column, with a 

 more or less shallow cartilage pit on either side, anterior muscular scar large, sub- 

 marginal, often situated on a projecting plate, posterior next to the hinder car- 

 tilage-pit, followed by two usually unequal projecting ribs or duplicatures of the 

 shell. Smaller valve opercule-like, flat or slightly elevated, with a central apex 

 and often variously punctated and porous; internally with two strong slightly 

 diverging hinge-teeth; the anterior muscular impression is situated on the side 

 of a strong tooth-like vertical projection and is usually divided into portions. 



Woodward explains the last duplicature of the lower valve as correspondino- 

 with the pallial sinus of other Pelecypoda. In a fine lower valve of H, radiosa, 

 for which we are indebted to the kindness of Prof. Hebert, there is a pit supported 

 by a column extending the entire length on each side of the hinge-rib, and a 

 somewhat internally projecting lamina extends from the median duplicature to 

 beyond the posterior one. Either this lamina was produced by an extension of the 

 posterior muscular impression or it really indicates a pallial sinus ; it is scarcely 

 possible to find another explanation for it. 



Woodward suggested two sub-genera of Hippm^ites, which latter name he 

 restricts to the typical species, such as H. Gomu-vaccinum, Bronn, or JB[. Loftusi, 

 Wd.; these having the hinge-rib well developed. 



