AMERICAN JOURNAL 



2. Note on Aturia Mathewsoni, Ciahh. 



This Cretaceous fossil of California is, I think, a member of 

 the Cretaceous genus Hercoglossa, Conrad. In all the species of 

 Aturia the septa are much more numerous than in Hercoglossa, 

 and unlike the septa of the latter, the angles of the lobes are 

 nearly in contact, and in the anterior portion of the shell over- 

 lap each other, whilst in the latter genus these angles are dis- 

 tant. I have no doubt therefore that the siphuncle of Mr. Gabb's 

 species will be found to be tubular as in Hercoglossa, and not 

 funnel-shaped as in Aturia. 



3. On CoRBicuLA DENSATA, Conrad. 



Prime, in his monograph of Corhiculadce,'^ remarks that all the 

 American species have a short sinus in the palleal line, whilst in 

 the exotic species this line is entire. In the only Miocene species 

 known in North America, the palleal line is entire, and the shell 

 belongs to the genus Corbicula, a genus unknown to the present 

 fauna of North America. In this exotic character the fossil 

 species accords with the present geographical distribution of cer- 

 tain genera of the American Miocene, as Crassatella, Clementia, 

 Bucardia, Isognomen and Glgcuneris, none of which genera are 

 known to be in the recent fauna of America. 



4. Description of a new genus of Pectinid^. 



LYROPECTEN, Conrad. 



Description. — Inequivalved ; both valves convex ; ears un- 

 equal ; ribs large ; ribs and intervening spaces striated ; hinge 

 with irregular oblique teeth on each side of the fosset; both 

 valves with a hump or wave on the umbo. 



L. crassicardo, Conrad, (fossil,) California. — Proceed. Acad. 

 Nat. Sciences, 1862, p. 291. 



Observations. — This genus made its first appearance in the 

 California Miocene. It is very different from the genus Pallium, 

 Klein, which is founded on Pecten pallium. The valves of that 

 species are regularly convex, and the hinge is without those 

 irregular teeth which characterize Lyropecten. Although I have 

 not seen hollow tubercles on the ribs of the fossil species, as in 

 Pecten nodosus, Lin., the latter is a species oi Lyropecten, together 

 with P. fragosus, P. suhnodosus, P. intermedius, P. magnificus, 

 and P. noduliferus, Sowerby. 



* Smithsonian Miscellaneous Collections, 8vo. 1865. 



