472 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



projection from its sides, some distance from its posterior end, instead of 

 being broader, deeply divided, and terminal, as in our shell. There are also 

 differences in the details of the other lobes and sinuses, but these are such 

 as might more probably be due to the different ages and sizes of the speci- 

 mens. 



Quite as strongly-defined differences may also be observed 1 between the 

 septa of the Indian shell and those of P. syrtalis, particularly in the nature 

 of the siphonal lobe, as may be seen by comparing our cut of the latter with 

 Dr. Stoliczka's figure. The differences are also here more worthy of con- 

 sideration, because both figures were made out from specimens not differing 

 to so great an extent in size. 



Whatever may be the relations, however, between these shells, I can- 

 not agree with Dr. Stoliczka that his Indian form is identical with the Texas 

 species, for which Dr. Roemer proposed the name A. Guadaloupce ; which 

 latter is not only a very much more convex form, but differs as strongly in 

 the nature of its septa from the Indian shell as our form and the typical P. 

 syrtalis do. I also regard both of the latter as distinct from Roemer's Texas 

 species, whatever may be their relations to each other, notwithstanding the 

 fact that Dr. Stoliczka quotes A. syrtalis doubtfully as a synonym of the 

 form he refers to A. Guadaloupce. 



I should also add here, that my friend Mr. Gabb, whose attention I 

 called to this subject, informs me that, after a critical comparison of Dr. Sto- 

 liczka's figures and description of the Indian shell referred by him to A. 

 Guadaloupce, with Dr. Morton's type of A. syrtalis, fully concurrs with me in 

 the opinion that these forms are specifically distinct from each other as well 

 as from the true Guadaloupce. We therefore agree that Blansford's name 

 Tamulicus should be retained for the Indian species, if it is specifically dis- 

 tinct from the form here described, and both can be separated specifically 

 from P. placenta. 



Locality and position. — The form 1 have here with considerable doubt 

 referred as a distinct variety to P. placenta came from Cheyenne River, at the 

 mouth of Sage Creek, Dakota ; where it occurs in (he Fort Pierre group of 

 the Upper Missouri Cretaceous. The Texas specimen, loaned to me by 

 Professor Martin, of New York, came from the Cretaceous rocks of Tarrant 

 County of that Slal.'. 



