338 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



Several authors, who acknowledge the identity of Turbonilla, and Chem- 

 nitzia, d'Orbigny, as the latter was first used, and that the former name has 

 priority of date, continue to use d'Orbigny's name for some of the extraneous 

 types included by him at the second date; but I hardly think this can be 

 properly done, as we have to go back to the original date to settle the question 

 in regard to the type of d'Orbigny's genus, and that makes it a synonym of 

 Turbonilla, Risso. Forbes and Hanley, who also admit the identity of Tur- 

 bonilla and Chemnitzia, and the fact that the former has priority, still retain 

 Chemnitzia for the Turbonilla group, mainly on the ground that the name 

 Turbonilla is, as they think, too nearly like those of some other widely 

 dissimilar genera. This, however, does not seem to me a valid reason for 

 rejecting Turbonilla for that group, as there is no danger whatever of its 

 being confounded with any of the similar names ; and there are many other 

 names as nearly like others already in general use, still retained without 

 inconvenience, in several departments of natural history. 



In 1850, however, d'Orbigny proposed (in volume II of his Paleont. 

 Franc. Terr. Jurass., page 30) the name Chemnitzia, de novo, for an entirely 

 different group of very much larger extinct shells with a non-reversed apex. 

 He did not here merely propose to extend the genus, so as to make it include 

 these larger shells, but, as stated above, proposed to use the name anew for 

 an entirely different group, acknowledging that his Chemnitzia of former 

 dates is a synonym of Turbonilla, and pointing out the distinctions between 

 it and his Chemnitzia of lb50. Authorities differ in regard to the use of an 

 abandoned name that has fallen into synonymy, in this way, for another genus; 

 some maintaining that it cannot be properly done, while perhaps a majority 

 of the most reliable authorities admit that a name that has fallen into 

 synonymy is free to be again used for another genus. If so, I can see no 

 reason why the author who first used it has not as good a right to use it 

 again, in such a case, for a different genus, as any one else. 



Even as thus used by d'Orbigny, at this last-mentioned date, however, 

 he evidently included species belonging to several distinct groups. His 

 C. condensata, for instance, with its auriculiform aperture and very decidedly 

 continuous peritreme, seems to represent a different group from the large 

 majority of his other species. The same may also he said of his C. Roissyi, 

 with its fiat whorls, quadrangular aperture, and distinct, open umbilicus. 

 I think it also probable that the short, smooth species like his C. carta 

 and C. vesta may likewise represent another distinct group, as may 



