[NVEKTEBRATE PALEONTOLOGY. 457 



peculiarities oi our stage <>l' development pass gradually into those of the 

 next. 



As I am not acquainted with the septa of the English* typical specimens 

 of A. Woolgari, which were not illustrated either* by Mantell or Sharpe, it is 

 of course possible that they may be specifically different from those of our 

 shell. Mr. Sharpe remarks that he had not clearly seen the septa of his 

 specimens, but adds that "they appear to have four or five trifid lateral 

 lobes." If he meant that they appeared to have that many lateral lobes on 

 each side, and the appearance was not deceptive, then, of course, our speci- 

 mens would belong to a distinct species. As he did not pretend, however, 

 to have clearly seen the septa in his specimens, I can hardly believe that 

 shells so very similar in all external characters could be so different in their 

 internal structure; and hence I can scarcely doubt that they are really spe- 

 cifically identical. 



As already suggested, it is more than probable that Ammonites Bramisi- 

 anus and A. Carolinus, d'Orbigny, are both synonyms of this species ; that 

 is, that these names may have been both proposed for young specimens of 

 this species in different states of development. Sharpe cites A. Carolinus 

 doubtfully in the synonymy of A. Woolgari; and it seems quite as probable 

 that the shell for which d'Orbigny proposed the name A. Bravaisianus may 

 be only a smaller specimen of the same. At any rate, I have before me spe- 

 cimens of the same size, showing the same simple keel and other characters, 

 and yet have others showing an unbroken series from these to the fully- 

 developed A. Woolgari, or, at least, to the species here identified with the 

 same. 



Locality and position. — Our figured specimens are from the southeast 

 base of the Black Hills, Dakota, where it occurs in the Fort Benton group 

 of the Upper Missouri Cretaceous series. The specimens described by Pro- 

 fessor Hall and the writer under the name Ammonites percarinai 'us came from 

 the same horizon on the Missouri, five miles below the mouth of Vermilion 

 River. It also occurs at this horizon in Northeastern Nebraska ; and I am 

 informed by Dr. White that he has found loose specimens of it in the Drift 

 of Northwestern Iowa. Dr. Newberry likewise brought specimens of it from 

 New Mexico, and Dr. Palmer found it eight miles north of Fort Lyon, Colo- 

 rado. I am not aware that it has been found in situ at any other horizon 

 than that above stated," in this country. 

 58 ii 



