FREE INSTITUTE OF SCIENCE 



7 >9 



TERTIARY FAUNA OF FLORIDA 



Lignitic or Chickasawan Eocene at Bell's, Greggs's, and Peach Tree 

 Landings, Alabama, and Fort Gaines, Georgia. 



This species is well distinguished by its narrow, simple, often distally 

 obsolete ribs, usually about twenty-four in number, with wider interspaces, thin 

 shell, small ears, and ovate form. 



Pecten (Chlamys) clarkeanus Aldrich. 

 Pcitcn I'liirkcanus Aldr., Harr., Hull. Pal., 2, p. 68, pi. 5, fig. II, 1895. 



Eocene of the Lisbon horizon, Sowilpa Creek, Alabama, Aldrich ; and 

 at Black Bluff Shoals, Brazos River, Texas, Lea collection. 



This species resembles worn specimens of P. u'alitiibbcaiins, from which 

 it differs by its more numerous (thirty to thirty-eight) ribs and its singular 

 habit of intermitting the production of ribs altogether at times, so that the 

 beak will show well-defined ribbing and a part of the disk be perfectly ribless, 

 while later on the ribs may appear again. It should be noted, however, that 

 only about three out of ten valves show the latter feature, the others having 

 continuous plain ribs from beak to margin. Some of the forms included by 

 Whitfield under P. Kneiskcrni may belong here. 



Pecten (Chlamys) nuperus Conrad. 



I'ct It'ii nupi-nts Conrad, Proc. Acad. Nat. Sci. Phila., vii., p. 259, 1854. 

 I\-i ten niipt'nim Conrad in \Yailes, Geol. Miss., p. 289, pi. xiv., fig. II, 1854. 



Jacksonian Eocene of Jackson, Mississippi, Conrad and L. C. Johnson ; 

 Montgomery, Grant Parish, Louisiana, Vaughan ; Russell's Springs, Decatur 

 County, Georgia, Pumpelly; also in the Vicksburgian at Arredondo, Florida, 

 Johnson. 



This species has been very generally confounded with P. perplanns 

 Morton, from which to a casual glance it chiefly differs by its chlamydoid 

 form. On more careful inspection, however, it will be observed that P. nuperus 

 has fewer ribs (circa twenty-two), which, though somewhat similarly scabrous, 

 are not accompanied by beaded lateral threads ; the ears are higher and 

 larger, the submargins wider, longer, and more conspicuous, and the radii of 

 the ears are formed by rows of sparse, fluctuated, little-elevated scales, rather 

 than by threads. The ribs of the disk in adults are keeled, with V-shaped 

 narrower interspaces, the whole sculptured with continuous, fluctuated, con- 

 centric, rather close-set, little-elevated, very thin lamella, which are usually 

 worn off more or less. In the right valve, as well as in young or worn speci- 



12 



