OEETACEOUS FOSSILS. 413 



has not been seen, the cast has all the features usually possessed by casts of 

 the typical forms of the genus. 



Formation and locality. — In Cretaceous beds on the Cheyenne River. 

 Probably from the Fort Pierre" Group. 



Genus ASTARTE Sowerby. 



ASTAETE EVANSI. 



Plate 11, fig. 13. 



Crassatella evansi H. & M., Mem. Am. Acad. Sci. and Arts, new ser., vol. 5, p. 383, 



PL 2, fig. 9. 

 Crassatella evansi (H. & M.) M. & H., Proc. Acad. Nat. Sci. Hist. Nov. 1853, p. 2 a. 

 Crassatella evansi (H. & M.) Meek, Smithsonian Check List Invert. Foss., p. 11. 

 Crassatella {Pachythcerus) evansi Meek, Pal. U. S. Geol. Snrv. Terr., p. 117, PI. 17, fig. 6. 



Shell of moderate size, triangularly-ovate in outline, with very ventri- 

 cose valves and strong projecting incurved beaks, which are situated ante- 

 rior to the middle of the valve; anterior and posterior cardinal margins 

 rapidly sloping from the beaks, and forming with each other a little more 

 than an angle of 90°, the anterior side being much shorter than the poste- 

 rior. Anterior and posterior extremities rounded; basal line less strongly 

 arcuate. Surface marked by concentric lines. 



On the internal casts the muscular imprints are of moderate size, ovate 

 and deeply marked, the pallial line simple and distinct, margin of the valves 

 crenulate. 



The species was originally referred to the genus Crassatella by the 

 authors, and we have seen specimens labeled by one of them as 0. {Pachy- 

 thcerus) evansi. We are not familiar with the characters of the genus 

 Pachythcerus, but can see no reason why this species should be classed else- 

 where than under Astarte, as it seems to have all the features of that genus, 

 and to be destitute of the internal cartilage pit of Crassatella. The exam- 

 ples in the collection before us are internal casts, and therefore we cannot 

 be entirely positive of all the external features 



Formation and locality. — In limestone at the top of the gray shales of 

 Cretaceous, No. 4, on the Cheyenne River, near Rapid Creek, Black Hills. 



