mi 



478 



NEW YORK STATE MUSEUM 



Genus trocholitoceras Hyatt 1894 



Hyatt's definition of the genus reads : 



This genus has been framed to inckide forms which are essentially 

 similar to Trocholites, but have the siphuncle ventrad of the center 

 in the earlier substages of development. 



The forms stand in development and adult characters between j 

 Litoceras and Trocholites. ^ 



Type is Trocholitoceras walcotti. 



Trocholitoceras walcotti Hyatt 



m 



Trocholitoceras walcotti Hyatt. Am. Phil. Soc. Proc. 1894. 

 32:480, pi. 6, fig. 12-20 



This form, which is cited as coming from Fort Cassin, has not been 

 observed by us in the Fort Cassin collections. Its ontogeny and adult 

 characters have been fully described and illustrated b}^ Hyatt in the 

 above cited publication. 



The appended transverse section [text fig. 37] 

 shows well its characteristic features, i. e. the 

 broad whorls of the young, which are kidney- 

 shaped in section while they become helmet- 

 shaped in section in the mature stage ; and the 

 close approximation of the siphuncle to the dor- 

 sum in the neanic stage. 



The living chamber occupies at least the 

 greater part of one half of a whorl and the 

 gerontic whorl does not become evolute. 



Genus trocholites Conrad emend. Schroder 



The term Trocholites has had an extremely 

 checkered career in its application to nautiliconic 

 cephalopods. It was first defined by Conrad^ in 

 1838; then in 1842^ the first definition was re- 



Both diagnoses lack 

 in precision and the term has therefore been 

 afterwards applied here and specially in Europe to a great number 

 and variety of forms. 



Remele [1889, p. 246] was the first to propose a restriction of the 

 application of the term to forms having the characters of the genotype 



Fig'. 37 Trocholito- 

 ceras walcotti 

 Hyatt. Transverse 



from Hyauf ^^°^^ vised by the same author. 



IN. Y. State Geol. An, Rep't 1838. p. 118. 

 2 Acad. Nat. Sci. Phil. Jour. 8:274. 



