110 rALJi:ONTOLOGY. 



examples of the species C. Icevldorsatus, but merely follow Mr. Gabb in refer- 

 ring- it to that form from the general resemblance to Professor Hauer's figures. 



After I had written the above, and refeired this species to C. Icevidorsatus, 

 liauer, Professor Hyatt sent me the following remarks in regard to this 

 species, which are worthy of quotation here, because they were drawn up 

 by liim after making direct comparison with authentic European specimens 

 of Dr. Hauer's species: 



"Gabb's figures and descriptions agree well with the Nevada speci- 

 mens in the collection, and his figure of the septa shows that the species 

 probably belongs to Clydonites. The agreement with Hauer's figure is not 

 so exact on account of the want of due exactness by which the pilse are 

 made to cross the abdomen in his figure, whereas in the specimens it is a 

 characteristic of late production. 



"Gabb especially states that in none of the specimens examined by 

 him did the pilse cross the abdomen. Hauer alludes to the need of a strong 

 side-light, in order to detect them in his specimens. This is by no means 

 the case with the ti\'0 full-grown Nevada specimens under consideration, 

 the abdominal pilse being very prominent in both. The young correspond 

 to the description alluded to in the California Report, which seems to have 

 been taken from a young specimen. The first of the adult stage of develop- 

 ment corresponds to Hauer's description, and a further development of the 

 abdominal pilje introduces the full-grown adult. All of these stages are 

 easily traceable; and the one very large specimen mentioned in the Cali- 

 fornia Report belonging to tliis species which did not have the abdominal 

 pilaj must have been an old specimen. In that case, it would have lost these 

 characteristics in the regular course of senile degeneration." — (A. H.) 



Locality and position. — Buena Vista Cailon, North Fork, Humboldt 

 Range, Nevada; Upper Trias (St. Cassian beds). 



" TRACE YCERATID^. 



"Genus GYMNOTOCERAS, Hyatt. 



"(;t'/i)'(if, naked; vuto;, back ; Ktpn^, a boni.) 



"The development of Ammonites Blakei, Gabb, and the characters of 

 its abdomen, separate it at once most decidedly from any species of Tra- 



