CRETACEOUS FOSSILS. 189 



numerous, fine, concentric lines of growth, and occasional irregu- 

 lar undulations. 



Figure, natural size. 



Locality : Tuscan Springs, Tehama County ; collected by Dr. Veatch. 



T. Evansii, Meek. 



PL 25, Fig. 177. 

 (T. Evansii, Meek. Trans. Albany Institute, vol. 4, p. 42.) 



Shell trigonal, produced behind; beaks anterior, subterminal, 

 very prominent, strongly incurved ; anterior end convexly trun- 

 cated, very broad laterally ; basal margin prominently rounded 

 in the middle, sloping upwards posteriorly straight to the poste- 

 rior end, which is narrow and round ; cardinal margin concave, 

 nearly straight behind. Corselet bordered by a rounded double 

 rib crossed by small transverse lines, and marked on its surface 

 by about eighteen or twenty small oblique ribs; remainder of 

 the surface marked by from eighteen to twenty-two large, pro- 

 minent ribs, slightly radiating, but nearly parallel posteriorly; 

 on very young shells, these ribs are pretty regularly nodose, but 

 become plain when the shell attains a medium size ; sometimes 

 the three or four posterior ribs show a faint groove ; interspaces 

 between the ribs regularly concave, and marked only by the 

 lines of growth which cross the whole surface. 



Figure, natural size. One specimen before me is between three and four inches 

 long ; but this size is rare. 



Localities : Common in Division A. Found at Tuscan Springs, Tehama County ; 

 Chico Creek, Butte County; Curry's, south of Mount Diablo; Benicia; Marti- 

 nez; Bancho de San Luis Conzaga, Pacheco's Pass; Jacksonville and Siskiyou 

 Mountains, Oregon; and Nanaimo, Vancouver Island. The specimen figured, 

 from Tuscan Springs, shows but eighteen ribs, and the lower portion of the buccal 

 margin is unusually prominent. There can be little doubt, however, of the 

 identity of the species, since I have found it very abundant at almost every 

 locality of the lower member of the Cretaceous of the west slope, from Nanaimo, 

 whence it was described, to Pacheco's Pass, a range of over seven hundred miles 

 in length. 



