404 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



when the ribs begin, and the change to Daonella takes 

 place. The Daonella stage lasts up to a diameter of a little 

 over five millimeters, when the anterior ear develops. 



Halohia stiperbais closely allied \.o H . fallax Mojsisovics, 

 but differs from it in the slightly coarser ribs, and the 

 smaller size at which the angle in the ribs occurs. It is 

 also nearly related to H . fascigera Bittner,^from the Karnic 

 stage of India; but the Indian species is as high as wide, 

 and more oblique in form, and the ribs are distinctly bun- 

 dled. The beaks are lower and scarcely projecting. The 

 ribs and concentric wrinkles appear to be stronger than on 

 H. super ba. 



Horizon and locality. Upper Trias, Karnic stage, zone 

 of Trofites subbullattis, of the Alps, and Shasta County, 

 California. It is common in this horizon in Shasta County, 

 on the divide between Squaw Creek and Pitt River. The 

 figured specimens came from Brock Mountain, six miles 

 northeast of the Bully Hill Mine, near the trail across from 

 Madison's to Brock's Ranch. The species is most abun- 

 dant in the calcareous shales just below the limestone with 

 Tropites siibbidlatus, but it is also quite common in the 

 limestone, where specimens with a width of one hundred 

 ten millimeters and height of about seventy millimeters 

 were found. 



Subgenus Daonella Mojsisovics. 



1874. Daonella, Mojsisovics, Ueber dieTriadischen Pelecypoden-Gattungen 

 Daonella und Halobia, p. 7. 



Type, Daotiella lommeli Wissmann. 



Equivalve, inequilateral, rounded in front and rear; beaks near the middle 

 of the hinge-line, and scarcely projecting above it. Surface of the whole 

 shell ornamented with radial bifurcating ribs. There are no ears, and this is 

 the chief character that separates Daonella from Halobia. 



Daonella appeared first in the lower Muschelkalk as an 

 offshoot from Posidonomya, but became common first in 

 the upper Muschelkalk, and lived on into the Karnic stage. 

 It seems to grade over into Halobia, so that most writers 



1 Pal. Indica, Ser. XV, Himalayan Fossils, Vol. Ill, Part 2, 1899, p. 45, pi. vii, fig. 15. 



