37 St. Maurice and Claiborne Pelecypoda 37 



T)'/^.— From Claiborne, Phila. Acad. ; Con. Coll. 



Horizons. — St. Maurice (abundant and large specimens ; 

 Claibornian, few and and small specimens.) 



Specimens figured. — Figs, i, 3, 4, 5, St. Maurice, La. ; Fig. 

 2, Hickcr}^ Miss ; figs. 6, 7, Claiborne sands, Claiborne, Ala. 

 All at Cornell. 



Localities. — Loidsiana : Sabine R., S. E. cor. Tp. 5 N. R. 

 13 W. ; St. Maurice ; well at Atlanta ; Winnfield, Ruston, Cal- 

 vin, Winona, Columbus, Marble Q'3'. Miss.: Wautubbee, 8 

 miles N. E. of Enterprise ; Hickory. Alabama : Claiborne 

 sands, Claiborne Bluff. 



Genus TRINACRIA 



On account of the varying outline of species belonging to 

 this genus the word Trinacria is somewhat misleading. Speci- 

 mens may vary from cuneate forms with a sharpl}^ defined 

 umbonal ridge to those ellipsoidal or nearly circular. Still there 

 are man)- features common to them all, and it seems impossible to 

 form natural subgeneric groups. The following constant features 

 may be noted : Taxodont hinge curved, Glycymeris-like, voxy 

 short in pointed shells, lengthening in transverse shells ; pit be- 

 neath the umbo triangular, developed almost wholly anteriorly 

 from the beak ; narrow and deep in cuneate forms, widely ex- 

 panded and vertically contracted in broader forms ; exterior 

 marked with fine radiate striations usually stronger in the gib- 

 bose species, almost obsolete in the flattish ; posterior with al- 

 ways a hint of truncation with a post-umbonal ridge and .slope, — 

 features which when projected in a post-basal direction bring 

 about the strong cuneate, carinate outlines already referred to. 

 The outline of these Eocene species being so various has caused 

 them to referred to several different genera by different authors 

 (see the various synonymies below) , but we see no good reason 

 for subdividing a natural group. 



Trinacria cuneus Conrad, PI. 18. Figs. 8, 9. 



Pectunculus cutieus Con., A. J. Sci., vol. 33, p. 342., Jan. 1833. 

 Nucula carini/era I^ea, Cont. to Geol. Dec. 1833, (Dec.) p. 198, pi, 6, 

 fisr. 212. 



