MERRIAM: TRIASS1C ICHTHYOSAURI A. 17 



lower portion (pi. 1, figs. 2 and 3). The upper part consists of very massive, 

 gray limestones. The lower beds are (Composed of dark gray or black, some- 

 what shaly limestones, and bands of calcareous black shales. Below the lower 

 division are the black Pit Shales of the Middle Trias. 



The Hosselkns Limestone contains in its fauna a. large number of inverte- 

 brate forms, of which the greater number of the species are Cephalopoda. In 

 addition to the Ichthyosauria, the vertebrates are represented by the thalatto- 

 saurian reptiles, and by a few fishes. 5 A list of the characteristic species would 

 include the following : 



Tropites s nil nil at us Hauer. Arc-estes pacificus Hyatt and Smith. 



Tropites dilleri Smith. Cosmonautilus dilleri Hyatt and Smith. 



l)ix<-i>h-i>i>ilcn s(ntdli)tgensis Hauer. Orthoceras shastense Hyatt and Smith. 



Sagenites herbichi Mojsisovics. Halobia superba Mojsisovics. 

 Juvavites subintermittens Hyatt and Smith. Tcrebratula, sp. indet. 



I'olycycliis Jiciiseli Oppel. Kltyiiclioiiclla, sp. indet. 



.(r/i<i<liltx i/<ibbi Hyatt and Smith. Myophoria, sp. indet. 



Calif ornitcs mcrriami Hyatt and Smith. Thalattosaurus alexandrae Merriam. 



Clionites compressus Hyatt and Smith. Thalattosaurus perrini Merriam. 



Sandlingitcs andersoni Hyatt and Smith. Nectosaurus halius Merriam. 



Sirenites lawsoni Hyatt and Smith. Ilybodus shastensis Wemple. 



Trachyceras lecontei Hyatt and Smith. Acrodus wempliae Jordan. 

 Hauerites asldeyi Hyatt and Smith. 



Ichthyosaurian remains have been found in nearly all horizons of the Hos- 

 selkus Limestone. They are nowhere very abundant, several years work hav- 

 ing brought in only about twenty good specimens. They are most numerous in 

 the Tropites subbullatiis, and Juvavites horizons near the top of the lower di- 

 vision. In the lower, more shaly beds little material has been found, but the 

 specimens occurring there were in good state of preservation and the elements 

 were not badly scattered. In a well-marked bed a short distance below the top 

 of the lower division many loose vertebrae and other skeletal elements have 

 been found associated with comminuted shells, evidently representing some- 

 what shallower water than the rest of the deposits. In the massive, gray beds 

 of the upper Hosselkus Limestone the remains are usually fragmentary and 

 scattered. Some large specimens showing connected parts of skeletons have, 

 however, been found there. 



As yet the genera Delpliinosaurus, Toretocnemus and Merriamia are known 

 only from the beds some distance below the top of the lower division, Shasta- 

 saurus occurs in both lower and upper divisions, but is represented in the 

 upper beds principally by the gigantic S. careyi. 



5 Merriam, J. C., The Thalattosauria. Mem. Calif. Acad. Sci., vol. 5, no. 1. 



Wemple, Miss E. M., New Cestraciont Teeth from the West-American Trias., Univ. Calif. Publ. Geol., vol. 5, 

 no. 4. 



Jordan, D. S., The Fossil Fishes of California, Univ. Calif. Publ., vol. 5, no. 7. 



