REPTILIAN AGE. JURASSIC PERIOD. 



77 



or divaricating striae on P. cottaldinus, of Sowerby, which to the unassisted eye 

 seems to be only marked with concentric lines. It is likewise even possible, we 

 think, that this genus may be found to include some Cretaceous species with straight, 

 rigid, radiating costse, such as P. galliennei and P. rotomagensis, D'Orbigny, for on 

 both of these shells, which are ornamented with straight, radiating costee, we observe 

 an entirely distinct system of curved, radiating, or divaricating striae, which on the 

 lateral margins cross the costse obliquely ; while these shells have the form and deep 

 byssal sinus of the typical Camptonectes. Still, they may present some differences 

 in the nature of the hinge or interior that, along with their surface markings, 

 would place them in a distinct genus. 



The typical species of this genus will be at once known from all the other groups 

 of Pectinidce, by their peculiar ornamentation alone. That these and various other 

 fossil and recent types usually referred to the genus Pecten, should be placed in 

 different genera from that group, as typified by the recent P. Jacobius, P. maximus, 

 &c., as maintained by Prof. Agassiz, cannot be reasonably doubted. 



This genus was introduced during the Jurassic epoch, and ranges through several 

 members of the Cretaceous system, the deposition of which it seems not to have 

 survived. 



Camptoncctes bellisti*iatu§. 



Pecten hellistriatus, Meek, Proceed. Acad. Nat. Sci. Phila. July, 1860, 311. 

 Camptonectes bellistriatus, Meek, Smithsonian Cat. N. Am. Jurassic Fossils, 1864. 



Shell Tery thin, compressed-lenticular, suborbicnlar ; valves nearly equally convex ; hinge line equalling two-fifths 

 to one-half the transverse diameter of the valves ; posterior ear very short or nearly obsolete, flat, and obliquely 

 truncated ; anterior ear larger, flattened, and marked by rather distinct lines of growth — in the right valve separated 

 from the adjacent margin by a more or less angular sinus one-third to one-half as deep as the length of the ear, 

 measuring from the beak. Surface strise very fine, regular, sharply impressed, and increasing in number by the 

 intercalation of others between as they diverge in extending from the umbonal region — so strongly arched as to run 

 out on the hinge line near the beaks ; concentric strise fine, regular, closely arranged, and often nearly or quite obsolete 

 on the flattened spaces between the impressed radiating strise, to which latter they impart a sub-punctate appearance. 



Length of a large shell, 2.65 inches ; breadth from hinge to ventral margin, 2.26 Inches ; convexity, 0.64 iuclt. 



A B £! 



Camptonectes bellistriatus. 

 A. Outside view of a small left valve. D. Enlargement of surface striae of same. B. Inside view of a large right 

 valve [the appearance of radiating markings within is an error in the engraving]. C. Outline of right and left 

 valves united. 



