26 Bulletin 31 26 



perhaps suggests. This fact has doubtless led Dall to consider a 

 much more rugged form from the Brazos River, Tex., as true 

 clarkea7ius {yrans.Ws.^. Ill, 739, '98). 



Not unfrequently valves of this species show a faint, broad, 

 quinque-costate structure (see figs. 10 and 11). 



Small specimens of this species in the iVcadeaiy Collection are 

 labelled P. frontalis Dall. This name Dall gave to take the place 

 of P. rogersi Clark which was pre-occupied. (See Trans. Wag., 

 pp. 731 and 753). Of the equivalenc}- of this Virginia form and 

 others from the Jackson of Miss, we cannot speak with authority. 

 Clark noticed his lapsus and renamed his rogersi, P. dalli, though 

 just after Dall had proposed the ndLmo. frontalis. The Va. forms 

 are doubtless closely allied to darkcaniis, but Aldrich's name has 

 three years priority over Dall's and Clark's. 



Type. — Aldrich Coll. Johns Hopkins Univ. Coll. . 



Horizon. — St. Maurice Eocene. 



Specimens figured. — C. U. Coll. 



Localities. — Sowilpa Cr. in type form (figs. 8 and 9). At 

 Hamilton Bluff and Lisbon often in abundance as small, almost 

 smooth, very thin and scintillatns-\\\i& specimens, though some- 

 times large and smooth or sometimes with evident costation. 



Pecten (clarkeanus? var. ) burlesonensis, n. var., PI. 14. Figs. 11, 12, 13. 



P. {Chlamys) clarkeanus Dall, Trans. Wag. Ill, p. 739, '98. 

 P. deshayesii Heilp., Proc. Phila. Acad. Nat. Sci., 1890, p. 403. 

 P. deshayesi Kennedy, Proc. Phila. Acad., &c., '95. 



This is the form in Texas that has usually passed under the 

 name of deshayesi in reports on Eocene paleontolog}' of the State , 

 but it is really much more nearly related to clarkeanus as described 

 elsewhere in these Bulletins. However, it is generally somewhat 

 higher, or narrower with a less expanding umbonal angle, thicker 

 or heavier, and with more pronouncedly radiately sculptured 

 \.\\dLX\. clajkeaniis. The surface about the umbones when smooth 

 have a somewhat worn appearance without the fine umbonal radi- 

 ation and the Camptonectes marking so well shown in clarkeanus. 

 The onl}' reason for referrring this io clarkea7i2is at all, is that, 

 although it is generally of the rather sharplv ribbed type, it does 



