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751 



TERTIARY FAUNA OF FLORIDA 



Pecten eboreus var. senescens I Jail. 



PI.ATK 29, FIGURE 5. 



Pliocene of the Waccamaw beds, South Carolina ; Johnson. 

 Shell of moderate size, rather convex ; ribs (twenty-three) obsolete exter- 

 nally, their line strong within ; the concentric sculpture fine, chiefly visible in 

 the interspaces. Alt. 60, hit. 62, diani. 15 mm. 



The posterior ear is a little more oblique in my specimen than in any of 

 the typical eboreus I have noticed, but the characters in general are so close 

 that I hesitate to regard the form as of specific rank. 



Subgenus PSEUDAMUSIUM H. and A. Adams. 



rscitdainnsiiim H. and A. Adams (after Klein), Gen. Rec. Moll., ii., p. 553, 1858. (Type 



P. hybriiiiis Gmelin.) 

 /'x,-itiiiiiniisiiiin Klein, Tent. Ostr., p. 134, pi. ix., fig. 11, 1753. Sole species. /'/<// 



/-,-/., vtirii-v-atus, etc., of Lister, pi. 173, tig. 10 ; Verrill, Trans. Conn. Acad., x., p. 



60, 1897. 



Ctiinfitmit'iti-s (Agassiz) Meek, S. I. Checkl. Jur. Fos., p. 39, 1864. 

 l-lhuriifopcctcn Conrad, Am. Journ. Conch., i., pp. 140, 190^, 1865. 



The type of this group is a very rare shell, which is chiefly found in old 

 collections, and was figured by Lister, from whom Klein copied his figure. 

 Since H. and A. Adams accorded Klein a place as a binomial author and cited 

 the genus as his, it follows that Klein's type and sole example was for them 

 necessarily the type of Pseiidamnsiiiiii, though they did not cite a type, and 

 included in their list several incongruous species. But as the evidence is 

 conclusive that Klein did not adopt the binomial system of his rival Linne, 

 the subgenus can only date from H. and A. Adams's habilitation of it in 1858. 

 The Listerian shell on which Klein based his name is identified by the elder 

 Sowerby and by Hanley with P. cxoticits Chemnitz (Conch. Cab., xi., pi. 207, 

 figs. 2037-8) and was named binomially by Gmelin, who called it P. liybndiis 

 in 1792, which is cited in their list by the brothers Adams. There is little- 

 doubt that it is also the P. dispar of Lamarck. 



As the shell is rare in collections, a summary of its characters may be useful. 



The surface is nearly smooth in the adult, the left valve being radially 

 and the right valve concentrically feebly sculptured. The latter is nearly flat, 

 with a well-developed ctenolium and byssal notch ; the ears in both valves are 

 small and have stronger sculpture than the disk. The surface has the Camp- 

 tonectes striation, most evident on the submargins. The hinge is simple, with 

 traces of the provinculum ; the cardinal crura in the left valve feeble and close 



