6l2 



NORTH AMERICAN INDEX FOSSILS. 





32. P. acutilirata Hall. Devonic. 



Umbilicus rather large and margins subangular ; sinus broad 

 and of moderate depth. 



Hamilton of New York, Pennsylvania, etc. 



XII. Bucaniella Meek. 

 Bellerophontoid shells with deeply trilobed dorsum, slightly em- 

 bracing, dorso-ventrally compressed volutions, sinuate aperture 

 without slit band, and faint surface striae. Siluric. 



33. B. trilobata Sowerby. (Fig. 818.) Siluric. 

 Small, strongly trilobed, the median lobe larg- 

 est ; sinus broad and shallow ; surface with fine 

 Fig. 818. Bu- revolving lines and lines of growth. 



Medina and Clinton of New York, Ohio, Penn- 

 sylvania, etc. Also Europe. 



caniella trilobata. 

 (After Hall.) 



XIII. Tetranota Ulrich and Scofield. 

 Bellerophontids with dorso-ventrally compressed shells, laterally 

 expanding aperture, open umbilicus, and sinus ending in a short 

 slit situated on a median revolving fold and flanked on either side 

 by one or more revolving ridges ; surface with sharp growth lines. 

 Ordovicic. 

 34. T. bidorsata (Hall). (Fig. 819, a-d.) Ordovicic. 



FlG. 819. a-d, Tetranota bidorsata (d = enlargement of surface); e-h y I, T. 

 sexcarinata (/= transverse section of whorl); i-k, T. obsoleta. (After Ulr. and 

 Scof., Pal. Minn.) 



