INTRODUCTIOX. 



Ill the course of the lirst investigation of the I'eptilian fauna of the 

 ( 'aliforuiaii Triassic, the w ritei' exainiiieil a peculiar jaw with a differeiitiateil (h'li- 

 titioii which was exposed on a specimen loaned t<i him for study by rrofessor 

 James I'errin Smith. This dentition was seen to reseml)h' the tigures of 

 Mirnfiaurns puhlished hy E. Frass/ and in a preliminary note on tiie Ichthy- 

 osauria of the ( 'alifornian Triassic" it was referred to that genus. Later prepa- 

 ration i-eveale(l the presence of other parts of the skeleton and showed a strueture 

 different from that of any ichtliyosaurian. This form was therefore not included 

 among the Ichthyosauria described later from the ('alifornian Triassic.'' 



During tlie Held seasons of 1002 and 1903, expeditions from the University 

 of California carefully worked over the greater portion of the Triassic limestone 

 exposures in Shasta ( 'ounty, and made special efforts to secure material from 

 whieh a satisfactor\- determination of the aflfinities of the unknown form could 

 be made. As the result of this work, a large collection of ichtliyosaurian 

 material was brouglit together and with it a considerable number of specimens 

 representing the new group. The preparation of this material has in all eases 

 been diffieult and has necessarily proceeded slowly, l>ut it has resulted in giving 

 us a fair representation of the most important tdements of the sktdeton. 



The acquisition of our knowledge of the Thalattosauria has been made 

 possible through the generous assistance of Miss A. M. .Mexander. who has not 

 only contribute(l the tinancial support of the field work, and in part also of the 

 preparation of the material for puldication, but was hers(df the discoverer of the 

 specimens which furnish the greater part of our knowle(lge of the fundamental 

 skeletal structure of the representatives of this grouj). 



Acknowledgments for \aluable services in connection with this investiga- 

 tion are also due to all the members of the University of ('alifornia licdd parties 

 which have worked on the Triassic limestones. To Trofessor .lames Perrin 

 Smith I am under obligation for the informatioii which led to the lirst ex[)lora- 

 tion of the Shasta limestones in search of saurian remains, and for the loan of a 

 valual)le type specimen. To Mr. K. L. l'\irloiig 1 am especially indebted for 

 v<'rv efficient assistance e.xtt'iiding through every stage of the work, from the 

 collection of the specimens to the final preparation of the material for study. 

 I'r. T. \\ . Stanton has loaned nii important sjx'cimen for study and description. 



1 E. Friiss, Ichthyosnurieid. deutschoii Trias & Jura Ablng., PI. in, figs. 1-4. 



2 Science. !i. ser. v. 1.5, p. 411. 



s See Triassic IchthyoptcrvKia. linll. I>ci>t. Ccnl. fiiiv. Calif, v. :J, no. 4, p. 8.'i. Dentition. 



