108 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [YolY. 



Ceplialopod forms from strata of the Western Territories which have 

 been assigned to the Trias as distinct from the Jura have been regarded 

 as especially representing the horizon of the St. Cassian, Aussee, and 

 Hallstadt deposits of Europe. The fossils referred to are those which 

 were obtained from the West Humboldt Eange, Nevada, and described 

 by Gabb in Vol. I of the Paleontology of California, and by Meek and 

 Hyatt in Vol. IV of the United States Geological Survey of the For- 

 tieth Parallel. 



Having recognized the unique character and Triassic type of these 

 Cephalopods, and the fact that, although closely related to typical Cera- 

 iifes, they presented some important generic modifications, I desired the 

 opinion of Prof. Alpheus Hyatt, whose excellent and exhaustive labors 

 upon this class of fossils are so well known. I therefore forwarded them 

 to him for examination, and have received from him the notes which, 

 on the following pages, appear in quotation-marks above his initials. 

 Professor Hyatt proposes one new genus, which has not only imj)ortant 

 and significant relations with other genera, but the fact is an interesting 

 one that with its first and only discovery three strictly conforming, but 

 well-differentiated species, were found associated together, indicating 

 thereby the j)ermanent establishment of that generic form. 



BEACHIOPODA. 



Genus Teeebratula Llhwyd. 



Terebratula semisemplex White. — Shell small, obovate or sub- 

 elliptical in margiaal outline; width less than the length •, cardinal slopes 

 gently convex or faintly angular ; margins of the shell obtuse ; both 

 valves somewhat regularly and nearly equally convex ; beak of ventral 

 valve moderately prominent, with the usual curvature over that of the 

 ventral valve, and with the usual apical perforation. Shell-structure 

 minutely punctate. Surface of both valves marked by numerous small 

 radiating plications, sometimes slightly irregular in size, with about 

 equally wide spaces between. These plications never reach the beaks, 

 and. sometimes extend only a short distance from the margins; the 

 remainder of the surface being plain, or marked only by faint lines of 

 growth. 



Length, 14 mOlimeters ; breadth, 11 millimeters ; thickness, 9 milli- 

 meters. 



The form and more especially the i^lications of this shell give it the 

 appearance of a Bhynclionella, but its punctate structure forbids its ref- 

 erence to that genus. Perhaps it is really a Waldheimia; but as the in- 

 ternal structure is not yet known, it is at present referred to Terebratula. 



Position and locality. — Jura-Trias strata, member A of the foregoing 

 section; at locality No. 1, Southeastern Idaho. Collected by Dr. A. C. 

 Peale. 



Terebratula augusta, Hall and Whitfield. — ^Among the collections 



