Mkrbiam.] 



New Ich Hi yosa u ria . 



259 



The mandible is constructed much like that of Ichthyosaurus, 

 with the exception that the supra-angular is somewhat larger, 

 taking up nearly the whole of the outer side back of the middle 

 of the orbit. The angular is visible on the outer side of the 

 jaw only as a very narrow strip near the posterior end. A cross 

 section of the mandible taken below the anterior end of the 

 lachrymal (PI. 23, lig. 3) shows a very large spenial extending 

 below the supra-angular, and a saddle-like section of the dentary 

 resting upon the supra-angular and overlapping it on the outside. 



In a section at the posterior end of the mandible (PI. 23, 

 fig. 2) there are shown the supra-angular, angular, and a large 

 element {ar) which can hardly represent anything other than 

 .the articular. This seems to be an elongated bone of consider- 

 able size. In addition to these there is possibly a fourth element 

 (,r), which resembles somewhat a bone doubtfully determined as 

 corresponding to the coronoid in Shastasaurus alexandra \ This 

 element is very indistinct and may not be separate from the 

 angular. 



Dentition. — Though many scattered teeth supposed to belong 

 to Ichthyosaurians have been found in the Oalifornian Triassic, 

 this is the first specimen to show the dentition in place in the 

 jaws. As is shown in Plate 23, figure 1, the slender conical 

 teeth are very numerous and closely crowded. As in Ichthyo- 

 saurus, they are inserted in rather shallow, open grooves 

 (PI. 23, fig. 3). There is no evidence that bony partitions 

 separate the teeth transversely as in Mixosaurus. As the maxil- 

 lary teeth are conical the dentition is evidently isodont. What 

 appear to be short and broad teeth near the posterior end of the 

 series in Plate 23, figure 1, are individuals which could be only 

 partly exposed in preparation, owing to their turning inwai'd. 

 As the teeth are softer than the matrix it has not been possible 

 to expose their surfaces satisfactorily, and the structure could be 

 studied only in cross-section. So far as can be seen, they are 

 not materially different from the teeth of Ichthyosaurus. 



Toretocnemus, New Genus. 



Vertebral centra elongated. Neural arches with lateral 

 ridge, not greatly thickened. Middle dorsal ribs with widely 



