i8o 



NORTH AMERICAN INDEX FOSSILS. 



section ; surface smooth or with numerous rounded, distinct costae 

 or undulations, strongest on siphonal side ; saddles and lobes, six 

 each, only slightly incised. 



Coloradoan (chiefly Niobrara) of Utah, Colorado and Texas. 



301. B. chicoensis Trask. (Figs. 1433, 1434.) Cretacic. 



Slender, of subelliptical section, with slightly narrower venter; 



X 



F'iG. 1435. Bactilites compresszis, side view and cross section. (After Meek.) 



ventral lappet proportionally longer and narrower than in preced- 

 ing species ; suture with narrow, bilobed saddles and broader lobes. 

 Nanaimo of Vancouver; Chico of California. 



302. B. anceps Lamarck. Cretacic. 



In form similar to B. gracilis, but with section more ovoid and 



