FREE INSTITUTE OF SCIENCE 



703 



TERTIARY FAUNA OF FLORIDA 1 -/ 



orthography by G;ibb and Fischer is unnecessary and contrary to the rules of 

 nomenclature followed in this volume. 



Notwithstanding the fact that the real type is intermediate in form 

 between the /'. vcntricosns group and that of I'. Jcffersonius, the balance of 

 characters is decidedly in favor of the latter, and, thus restricted, it forms a 

 fairly natural and recognizable assembly which will contain, besides the type, 

 such forms as /*. crassicardo Conr., l y . Jcffersonius Say, /'. Madisonius Say, P. 

 edgecombensis Conr., l\ septenarius Say, all large species, with conspicuous 

 ribbing, radially squamose-striate surface, convex and nearly equilateral valves, 

 and more or less developed cardinal lamina:. The group is chiefly Miocene. 



In Pecten Clintoniits we have a species which appears to differ remarkably 

 from such forms as Jcff'crsonins, and yet the most essential distinction is the 

 absence of ribbing. If we were to imagine a specimen of P. Jcffersonius with 

 the ribs flattened out, the distinction between it and P. Clintomus would be 

 almost imperceptible. In recent Pectens the group is only represented by 

 such forms as P. fuscopnrpiirens Conrad, which never attain a large size but 

 resemble in their sculpture the young shell of /'. Madisoitiiis and its allies. 

 They can hardly be accommodated in the group as here restricted. 



Pecten (Plagioctenium) deserti Conrad. 

 1',; t,-n ii,-s,'rti Conr., 1'ac. 1\. R. Rep., v., p. 329, pi. 8, fig. 77, 1856; Descr. Fos. and 



Shells, House Reps. Doc. 129, p. 15, July, 1855. 



/'t't'tt'ii (/is, us Cooper, Cal. State Min. Ikir. Dull., No. 4, p. 57, pi. 4, tigs. 55, 56, 1894 ; 

 not /'. disfits Conrad, 1857. 



Miocene (?) of Carrizo Creek, Colorado Desert. 



This appears to be a well-defined species resembling P. turgidns Lamarck, 

 having twenty-three close-set, smooth, rounded, prominent ribs, and both 

 valves moderately convex ; the specimens are usually crushed. This has 

 been confounded by Cooper with /'. discus Conrad, his remarks showing that 

 Dr. Cooper is unacquainted with the true /'. discus. 



Pecten (? Plagioctenium) pabloensis Conrad. 

 /',;/,/! /in/'/i v//.v/\ Conr., Par. K. K. Reps., vi., p. 71, pi. 3, fig. 14, 1857. 



Miocene of San Pablo Bay, California ; Merriam. 



This species is represented by a better figure than some of the others, 

 and has been collected from the original locality by Dr. John C. Merriam, 

 of the University of California. It has been erroneously referred to the 



