382 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Diameter 42 mm. 



Height of last whorl 21 mm. 



Height of last whorl from the preceding 17 mm. 



Width of last whorl 13 mm. 



Involution 4 mm. 



Width of umbilicus 8.5 mm. 



Horizon and locality. Upper part of Middle Trias, 

 Daonella beds, West Humboldt Range, Nevada, on the 

 divide between Troy Canyon and the south fork of Ameri- 

 can Canyon, associated with Ceratites vogdesi, Anolcites 

 meeki, A. whitneyi, A. hyatfi, Beyrichites rotellifor^nis, 

 Daonella dtcbia, and many others. The specific name is 

 given in honor of Mr. L. F. Dunn, of Winnemucca, Neva- 

 da, to whom the writer is indebted for the discovery of 

 this locality. 



Genus Ceratites de Haan. 



Type, Ceratites nodosus Brugiere, figured by de Haan in his Monographias 

 Ammoniteorum et Goniatiteorum Specimen, 1825, p. 39. 



This genus, which is the commonest and most widely dis- 

 tributed of the Middle Triassic ammonites, as well as the 

 most characteristic, is the hardest to define. After de Haan 

 introduced the name Ceratites, all ammonites with ceratitic 

 septa were assigned to this genus, thus including species 

 from the most diverse genera and even families. The type 

 species is common in the Germanic basin, but until recently 

 was unknown outside of the province, and so most writers 

 that have dealt with Ceratites have described species from 

 other provinces and other regions. It could not be expected 

 that they would all agree with the type, and hence these 

 writers have had free rein to extend the genus as it pleased 

 them. They have extended the genus, which was allowable 

 and necessary, but there has been little uniformity in their 

 extensions. Further than this, they have overlooked the 

 fact that the original type must be considered as the typical 

 form, and in many cases have come to regard the group of 

 Ceratites nodosus as exceptional, and the Asiatic and Alpine 

 species as normal, which was unwarranted. 



