Merriam.] 



New Ichthyosauria . 



253 



carefully described and additional forms have been obtained from 

 the Triassic of California, it becomes a much more difficult 

 matter. To settle it satisfactorily involves a discussion of the 

 primitive characters and the course of evolution of the Ichthyo- 

 sauria. This is deferred to a study of the subject to appear in a 

 later paper. 



DETAILED DESCRIPTION OF NEW GENERA AND SPECIES. 



Leptocheirus. New Genus. 



Caudal vertebrae elongated. Dorsal ribs single-headed. 

 Coracoid shield-shaped, much elongated antero-posteriorly, 

 without anterior or posterior emargination. Extremities with 

 three slender digits and rudiment of a fourth. Anterior limb 

 much larger than posterior. Elements of the propodial and epi- 

 podial segments of anterior and posterior limbs much longer than 

 broad. Epipodial bones separated by a wide cleft. Bones of 

 first and third rows of the inesopopial, metapodial, and phalangeal 

 regions all notched on one or both sides. Carpus and tarsus 

 with linear arrangement, three elements each in the in the prox- 

 imal and distal rows, intermedium articulating distally with but a 

 single bone. Dentition isodont, conical teeth set in open grooves. 



Leptocheirus zitteli n. sp. 



Pls. 21, 22, and 23. 



The type specimen (No. M 8099, University of California 

 Palseontological Museum) is represented by the lower half of a 

 skull with a part of the dentition, the complete pectoral girdle, 

 both anterior limbs, and numerous fragmentary ribs, vertebrae, 

 and abdomiual ribs. It was discovered by Miss A. M. Alexander 

 in the Trachyceras zone of the upper Triassic limestones at the 

 Cove near Madison's Ranch on Squaw Creek, Shasta Co. 



Vertebrce and ribs. — The only well-preserved vertebra present 

 is an anterior caudal (PI. 23. fig. 4) with the following dimen- 

 sions: length 14 mm., height 22 mm., greatest width 24 mm. 

 The end faces are very deeply concave, sloping sharply from the 

 periphery and almost meeting in the center. The diapophyses 

 are small but have considerable lateral projection. The articular 

 surfaces for the reception of the lower arches are situated on 



