'J^)S CABHONIKKKOUS FORMATIONS AND FAUNAS OF COLORADO. 



iiai TOW ami sliallow, a linear iiiciliaii depression. None of the shell sexiiiniiie(l attain 

 either the size or the development of fold and sinus of mature e.xamples of S. snh- 

 guadrafa, but they follow, with agreement singularly exact, the young and adolescent 

 stag^es of that species. Comparison has been made with specimens characteristic of 

 S<-))i/')iidfi siihquadnifd from Pope County and from Chester, 111., and the closest 

 agreement was found. 



This form somewhat resembles the rounder specimens of Crana&na suhelliptica 

 var. hardingensis, and suggests a doubt of the generic reference, which probably 

 would not otherwise be questioned. No specimen perfect enough to retain such 

 characters which is at the same time certainlj^ a dorsal valve has been observed, but 

 this valve seems to have had no internal structures of a septal nature. The ventral 

 valve shows two rather weak dental plates. 



Compared with less elongate specimens of GransRna s^d)elliptica var. harding- 

 e)isis this shell is smaller and more quadrate, and it possesses a faint though distinctly 

 discernible fold and sinus. In the ventral valve the plates ai-e less strong as a rule and 

 farther apart, and the umbonal portion has not, seemingly, the peculiar and charac- 

 teristic conformation of the terebratuloids. 



At Perry Park (station 3367) there occurs in considerable abundance a small 

 species of Semmula that 1 believe can be referred only to the species to which the 

 material from Leadville belongs. None of the examples from Perrj^ Park are as 

 large as the larger ones from Leadville, but with such as are of their own size they 

 agree complete^. This identification is in a measure confirmed bj' the circumstance 

 that these shells at both localities occur associated with a peculiar and probably new 

 species of Spirifer. These specimens might be placed with Seminula humilis or with 

 *§■. vjosatchensh^ but probably with less precision. The ventral beak of S. humilis 

 is larger and more tumid, and where the thick shell is removed the internal cast 

 shows the presence of a deep rostral cavity, imparting to these molds a different 

 shape from those from Perry Park, for the, specimens from that locality occur in this 

 condition. 



Seminula hmrulis and S. wasatchensis, of which mention is made above, are 

 closely similar, and were it not that the latter is founded upon a solitary specimen 

 whose horizon is .still in doubt and may be very different from that of S. humilis 1 

 would not hesitate to throw them together. 



Although Semimda sxdyquadrata was described from rocks of Genevieve age, and 

 although it was especially abundant during that period, the identification of it in the 

 upper beds of the Leadville limestone can not be considered as entirely diagnostic of 

 their geologic age, since a ver}^ similar shell occurs in the Cuyahoga shale of Ohio, 

 which probably belongs to the Osage period. 



Locality and horizon. — Leadville district (stations 2375, 2377, 2378); Leadville 

 limestone. Castle Rock quadrangle (station 2367?); Millsap limestone. 



