398 NORTH AMERICAN INDEX FOSSILS. 



Characteristic of the Maquoketa shale of Illinois, Iowa, Wis- 

 consin, Minnesota. 



82. N. oblongatus Conrad. (Fig. 509, a-c.) Devonic. 

 Elongate-ovate, widest anteriorly. Beaks appressed and low. 



Surface marked by very fine concentric striae. 



Very abundant in the Hamilton : New York, Pennsylvania, 

 Virginia. Also present in Marcellus of New York and Portage 

 of Pennsylvania. 



83. N. triqueter Conrad. (Fig. 509, d-f.) Devonic. 

 Distinguished by its trigonal form, prominent arching beaks and 



strongly arching umbonal ridge. 



Very abundant in the Hamilton : New York, Pennsylvania, Vir- 



/ A i ji n 



a 



Fig. 509. a-c, iVuculites oblongatus ; d-f, A', triqueter. (N. Y. Surv., V.) 



ginia, Ontario. Also present in the Marcellus of New York, and 

 Portage of Pennsylvania. 



XXVIII. Pal,eoneilo Hall. 



Shell Nucula-\\ke, with extended anterior and posterior ends, 

 and more or less defined depression along the umbonal slope. 

 Ligament external and contained in narrow groove along the car- 

 dinal border. Pallial line simple. 



Differs from Nuciila, Leda and Yoldia in the absence of a resili- 

 fer beneath the beak and in having an external ligament and a 

 post-umbonal depression externally. Differs from Nuculites in the 

 absence of the internal anterior ridge. Devonic-Triassic. 



84. P. muta Hall. (Fig. 510, £--z.) Devonic. 



Varying in outline from more to less elongate, and thus resem- 



