266 PALAEONTOLOGY OF CALIFORNIA. 



researches of Dr. Roemer a*nd Mr. Conrad, have demonstrated the existence of 

 several well-characterized and peculiar genera in the Cretaceous and Tertiary, 

 among forms, until recently, referred to modern genera; and were our material 

 more perfect, I am convinced that still further separations would be required. 

 Palaeontological conchology is shamefully in the rear, in the matter of generic 

 division, as compared with that portion of the science which relates to living 

 forms ; and although palaeontologists have a good excuse for their conservatism, in 

 the very frequent total or partial absence of characters, yet when the material 

 under consideration does retain all of its distinctive characters, they are too apt to 

 allow their fear of radicalism, on the side of excessive subdivision, to drive them 

 into the no less blameworthy fault of " old fogyism " on the other extreme. 



It is in view of this failing of my co-laborers in the field of fossil conchology, 

 that I have proposed so many new genera and sub-genera in the present work. I 

 hardly hope that, for the present, all of them will be adopted, though they are 

 certainly as distinct as the average of the modern genera, universally acknowledged 

 by the students of the existing malacological fauna. 



CARDIUM, Linn. 



GRANOCARDIUM, New S. Gen. 



I propose the present, subdivision of Cardium to receive a well- 

 marked, though small group, of shells in the genus, characterized 

 by a peculiar style of surface ornament. They seem to be pecu- 

 liar to the upper portions of the Cretaceous formation, the oldest 

 species with which I am acquainted being found in the upper 

 Green Sand. The subgenus may be described as follows : Shell 

 nearly equilateral, usually longer than wide; valves closed all 

 round ; surface ornamented by two series of radiating ribs, large 

 ribs bearing spines, tubercles, or grains, and smaller ribs occupy- 

 ing the interspaces between the larger, aud also granulate. 



This is one of the most highly ornamented groups in the genus, and is repre- 

 sented in Europe by C. produciu??i, Sby., C. Moutoniannm, d' Orb, and C. Carolinian, 

 d'Orb, and in America by C. Tippcmum, Conrad, and the present species. Tippanum 

 is from the equivalent of the upper chalk, sabulosum is on the horizon of the lower 

 chalk, and the three European species quoted, are from the upper Green Sand, 

 (Ccitomanien, d'Orb.). 



The ornaments of the present species are more minute than on any of the others 

 in the subgenus, with which I am acquainted. 



