TRIASSIC FOSSILS. 21 



GONIATITES, De Haan. 



(? AGANLDES, Montf.*) 

 G. l^vidorsatus, Hauer, sp. 



PI. 3, Figs. 6, 7. 

 (Ammonites Id., Hauer; Sitzungsber. K. Akad. Wien, 18G0. PI. 3, figs. 9, 10 b.) 



Shell discoidal, whorls many; increasing very gradually in 

 size ; each, volution enveloping about one-fourth of the preceding 

 one. Umbilicus broad and shallow. Aperture sub-elliptical; sides 

 sometimes nearly straight, emarginate on the ventral side. Sur- 

 face sometimes plain, sometimes strongly ribbed. When the 

 ribs are present, they arise on the margin of the umbilicus, and 

 arch forwards as they approach the dorsum ; but always become 

 obsolete before reaching it. 



They present every variety, from sharp, prominent ribs, to al- 

 most obsolete undulations, usually being more closely placed in 

 proportion to their distinctness. 



Septum composed of a dorsal and two lateral lobes, which, 

 with their saddles, are all mere rounded undulations. Hauer, 

 when he described this species, had not seen the septum. 



Dimensions : Diameter across the body whorl, 1.05 inch. 

 Width of body whorl, .32 inch. Width of aperture, .25 inch. 



These measurements are from the specimen figured. It possesses five volutions. 

 Another specimen, 1.75 inch in diameter, has eight whorls. The specimen figured 

 differs somewhat from Hauer' s figure in the transverse diameter of the whorls ; 

 but still greater differences exist between specimens found at our locality, both in 

 this respect and in the prominence and distance between the ribs. Prof. "Whit- 

 ney collected in El Dorado Canon, near Dayton, "Washoe, a species which may be 



* It is doubtful whether this name should be accepted. The description given 

 by Montfort was so indefinite that it might be applied with equal or even greater 

 propriety to the genus Cbjmcnia. I prefer, therefore, to adopt the name given by 

 the first author, who characterized the genus properly; especially since, with the 

 exception of d'Orbigny, all subsequent authors have given it their sanction. 



