104 



A. HYATT — GEOLOGY OF THE TAYLORVILLE REGION. 



than in the Hardgrave sandstone Lima dilleri and L. taylorensis, Ctenos- 

 treon, Trigbnia and Entolium arc ant t<> occur in all the outcrops. So far 

 as the determination of age is concerned, however, the ammonitinae, 

 although not abundant, afford the best evidence. These highly special- 

 ized forms, as has been pointed out by several of the most distinguished 

 paleontologists, in Europe, must have been extremely sensitive to the 

 influence of the changes of the surroundings in passing from one geologic 

 level to another, and have recorded these mutations in their own organi- 

 zations. Even the encyclopedic Quenstedt continually expresses his 

 satisfaction in turning from the uncertain indications afforded by the 

 more generalized structures of other mollusca to the decisive chronologic 

 evidence usually given by the fossils of this group. The list printed 

 below contains a series of selected species, hut many forms, especially 

 among the smaller pelecypoda, which have not yet been studied, are 

 necessarily omitted : 



Taylorville, California. 

 Terebratula. 



Rynchonella, n. sp. 



Alectryonia, n. sp. 



Modiola subimbricata, Meek, and 

 also other species of the same 

 genus similar to this, but hav- 

 ing shorter and broader shells. 



Mytilus, n. sp. 



l'iii mi film iformis, n. sp. 



I'ti roperna, n. sp. 



Europe. 



Terebratula perovalis, Sow., as figured 

 and described by Quenstedt, is 

 similar, but the American species 

 has no dwarfed varieties: inferior 

 Oolite. 



Rynchonella quadriplicata, Zeit., as 

 figured and described by (Quen- 

 stedt; great Oolite. 



Orthis marshii, Goldf.. as figured by 

 Mor. et Lye. in Oolite Mollusca; 

 inferior and great Oolite. 



Modiola imbricata, Sow., and other 

 species of Modiola, with heavy 

 umbonal ridges, occurring in the 

 inferior and great Oolite. 



Mytilus sublsevis, Mor. et Lye, and 

 other species, having arcuate forms 

 and heavy umbonal ridges, which 

 are characteristic of the Oolite. 



Pinna cuneata, Phill., as figured by 

 Mor. et Lye. in Oolite Mollusca ; 

 inferior Oolite. 



Stands between Pteroperna phi mi and 

 Pteropema costalula, Mor. et Lye; 

 inferior and great Oolite. 



