.MKKKIAM: TRIASSIC ICHTHYOSAURIA. 19 



nated with iron oxide. In a few localities of comparatively small area the ich- 

 thyosanr skeletons are very numerous. The writer is not aware of any local- 

 ity in other formations at which remains of ichthyosaurs are more abundant. 



At American Canon, where the most extensive work has been carried on, the 

 beds have fortunately been repeated twice by faults, giving a large exposure of 

 the most fossiliferous strata. In this region, between thirty and forty good 

 specimens were obtained on Saurian Hill, and from the same bed repeated on 

 Fossil Hill farther to the east. 



In many cases there seems to be a concretionary formation about the skele- 

 tons. This is mostly distinctly shown in the case of the skull, which may be en- 

 closed in a rounded nodular mass. This structure is noticeable also in follow- 

 ing the vertebral column, the layer containing the vertebrae often pinching out 

 on both sides of the skeleton. Unfortunately the ends of the limbs seem often 

 to have extended beyond the nodular envelope, and are not to be found in the 

 rock immediately outside of it. 



The Triassic beds in the New Pass Range are of nearly the same age as those 

 in the West Humboldt Range. The exosures are not as extensive as in the 

 West Humboldt Range and the beds are hardly as rich in fossils. 



The following are, according to Professor Smith, the most characteristic 

 species of this locality: 



Celtites ncmnari Mojsisovics. Ceucoceras bonae-vistae Hyatt and Smith. 



Ceratites (Paraceratites) trinodosus Mojsisovics. Arcestcs gabbi Meek. 

 Trachyceras americanum Meek. Gymnotoceras blakei Gabb. 



In the New Pass Range thirty miles west of Austin and three miles west 

 of the New Pass mine several parts of ichthyosaurian skeletons were obtained. 

 The first specimen of a Middle Triassic ichthyosaurian to be described from 

 America was found at this locality (Leidy, 1868). 



The Middle Triassic limestones are represented at other points in Nevada, 

 and will probably be found to have ichthyosaurian remains more or less abun- 

 dantly represented in them wherever they occur. 



Though it is probable that the Ichthyosauria had become marine forms as 

 early as Lower Triassic time, no one has yet succeeded in obtaining in Amer- 

 ica any material representing the group from beds lower than the middle divi- 

 sion of the Trias. The marine Lower Trias of eastern California and partic- 

 ularly of southeastern Idaho is very rich in fossils, including cephalapods, with 

 which ichthyosaurs are elsewhere associated ; but as yet no bones have been ob- 

 tained which can be referred to reptilian orders. Bones of crossopterygian 

 fishes are fairty common in these beds 7 in association with cephalapods. 



t Goddard, M., Fish Eemains from the Marine Lower Triassic of Aspen Ridge, Idaho. Univ. Calif. Publ. 

 Geol., vol. 5, no. 8. Also, Evans, H. M., A New Cestraciont Spine from the Lower Triassic of Idaho. Univ. 

 Calif. Publ. Geol., vol. 3, no. 18. 



