INVERTEBRATE PALAEONTOLOGY. 



371 



Among all of the published foreign species, this seems (o be most nearly 

 represented by Pyrula cancellata, Sowerby, as illustrated by Dr. Stoliczka in 

 the Palaaont. Indica, II, plates 12 and 13. It is readily distinguished from 

 that species, however, by its longer canal, less strongly angular body-volution, 

 smoother surface, and by its aperture being merely about rectangular at the 

 connection of its outer lip with the body-volution above, instead of pinched 

 up so as to form a kind of notch there. 



The specific name of this fine species was given in honor of Prof. 

 Spencer F. Baird, the able and well-known naturalist of Washington City, 

 and assistant secretary of the Smithsonian Institution. 



Locality and position. — Fox Hills and other localities near Moreau 

 River; in the Fox Hills group of the Upper Missouri Cretaceous series. 



Pyropsis Bairdi, var. r otiila, M. 



Fig. 47. 





Plate 31, fig. 10, c, and annexed cut. 



This form has long been something of a 

 puzzle. I have frequently been nearly satisfied 

 that it ought to be separated specifically from 

 the last, but, after careful comparison, have 

 always been left in doubt whether it may not j| 

 more properly be only a variety of the same. 

 This question, however, can only be definitely 

 settled by the study of more extensive collec- 

 tions than have yet been obtained. Its most 

 striking differences are the more depressed, or 

 less ventricose, form, and more angular outline 

 of its body-volution, which also has its third, 

 or lower carina, less prominent than in the 

 last, or sometimes even wanting. The upper 

 slope of its body-volution also differs in being 

 flat, or even slightly concave, instead of a little 

 convex. Its revolving striae are likewise more 



also, the appearance of the columella, 

 numerous, and uniform in size; none of those &c.,when the inner lip is partly broken 



on the under side of the body-volution being away ' 



larger than the others, or assuming the character of little ridges, as in the 



Pyropsis Bairdi, var. rotula. 



A view showing the more rounded 

 form of the aperture in this variety; 



