49 St- Maurice and Claibokne Pelecypoda 49 



lines if present are confined to the margins (see fig. 13). There 

 is an early, Li)iiopsis-\\\ie, stage, generall}' separated off from 

 the adult stage by a sharpl}' incised growth line. General ap- 

 pearance of the adult ribbing is similar to that of the Sabine spe- 

 cies usuallj' referred to idonca. 



Types divA specimens figured. — Paleont. Coll. Cornell Univ. 



Horizon. — St Maurice Eocene. 



Localities. — Lisbon, Ala. ; Wautubbee, Miss. 



Giycymeris trigonella Conrad, PI. 20. Figs. 1,7. 



Pedunculiis trigonella Con., A. J. Sci., vol. 23, 1833, p. 342. 

 Pirtuculus deltoideus L,ea, Cont. to Geol., Dec, 1833, p. 77, pi. 3, fig. 



55- 

 Axinea trigonella Con., A. J. Conch, vol. i, 1865, p. 12. 

 Pectunculus deltoidiisAe Gre^., Mon. Faun. Eoc, Ala., 1890, p. 194, 



pi. 23, figs. 15, 16, 32, 38, 42 ; pi. 24, figs. I, 2, 3. 

 Pcctiinciilns trigonetlus Har. These Bulletins, vol. i, 1895, p. 46. 

 Giycymeris trigonella Dall, Trans. Wag. &c.. Ill, 1895, p. 606. 



Conrad's original description. — Shell subtriangular, elevated, with 

 radiating striae ; anterior margin nearly rectilinear and subangular at the 

 extremity ; inner margin serrate. Length, half an inch. 



Locality. — Claiborne, Ala. London clay. 



This is a very abundant shell in the Claiborne sands and one 

 which seems to be in that same plastic state shown by species of 

 Venericardia in the Midway. Full-grown specimens average 

 about 10 mm in greatest diameter, but some may attain a height 

 of 14 mm. Some are very cuneiform, others nearly circular ; 

 .some with sharply defined ribs, some with faint ribs or none at 

 all ; .some with coarse marginal crenulation, often coarsest med- 

 ially, some with much finer crenulation. 



The more circular forms, with finer marginal crenulation re- 

 ceived the specific name of minor from Lea (figs. 6, 7). Such 

 forms are usually nearly smooth exteriorly, as Lea's tj^peinthe 

 Phila. Acad. Collection is. (Ribbing must have been put in 

 from another specimen b}" the artist. See Lea's fig. 54.) 



Most Claiborne specimens are considerably worn and the rib- 

 bing is somewhat obscured. Naturally the more faintly ribbed 

 specimens would appear more nearly smooth and these may be 

 thought of as con.stituting a variety minor. Yet in some cases 



