BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 479 



T . am m onius ; while Hyatt at first [1884, p. 267] inclined to 

 extend the diagnosis so far as to include all forms hitherto desig- 

 nated in Europe as " Imperfect Lituites " with dorsal or subdorsal 

 siphuncles. 



Schroder in 1891 [p. 5 fr] restricted the genus to its original 

 limits and fully defined it; and Hyatt adopted [1894, p. 482] this 

 definition which we insert here in translation as the correct one : 



Conch symmetrically involute. Living chamber completely con- 

 tiguous with preceding volutions, occupying about three fourths of 

 a volution. Section always wider than high. Aperture expanded, 

 with ventral sinus. Sutures simple or little lobed. Siphuncle dorsal, 

 or subdorsal. 



The ontogeny which had already been investigated by Holm and 

 the generic relations of Trocholites are fully discussed in Hyatt's 

 above cited publication. 



Trocholites internestriatus Whitfield (sp.) 



Plate 24, figure 2 



Lituites internastriatus Whitfield. Am. Mus. Nat. Hist. Bui. 



1886. v. 1, no. 8, p. 332, pi. 29, fig. 5-8 

 Discoceras internestriatum Schroder. Pal. Abhandl. von 



Dames und Kayser. Bd 5, Heft 4, p. 23. 

 Trocholites internastriatus Hyatt. Am. Phil. Soc. Proc. 1894. 



32:485, pi. 4, fig- 25 



This single representative of the genus Trocholites in the Beek- 

 mantown fauna has not been observed in the beds at Yalcour or 

 anywhere else on the west shore of Lake Champlain and is thus far 

 restricted to the outcrop at Fort Cassin. 

 We have figured a specimen, which has 

 been collected by Professor Perkins and 

 which exhibits the absence of ribs on the 

 nepionic stage and their somewhat abrupt 

 appearance at the end of this stage better 

 than any other specimen that we have ob- 

 served. It also shows well the relatively 

 large size of the umbilical perforation, a 

 feature in which this sbecies differs from its Fi? - 38 Trocholites 



1 internestriatus 



later congeners [sec pi. 24, fisr. 2, and en- Whilf : isp.) Kniarge- 



L 1 t> a > ment (x 2) of first two vo- 



lar ^vment of central part in text fi<r. ^81 . lutions to show changes 



1 o o J of sculpture 



Whitfield saw the most distinctive fea- 

 tures of the form in the surface undulations and striae and specially 

 in the internal striations. The markings resemble those of Trocho- 

 lites according to Hyatt with which genus it also has in common 



