PELECYPODA—PRIONODESMACEA. 445 



flattened beaks which are also not so oblique and are more distant 

 from the anterior end. 



Pierre : Rocky Mountain region. 



220. I. barabini Morton. Cretacic. 

 Moderately gibbous anteriorly, cuneate posteriorly. 

 Abundant in Pierre of Rocky Mountain region ; also in Fox 



Hills formation. 



LXVIII. Pteria Scopoli. {Avicnla Bruguiere.) 



Obliquely oval, inequilateral, inequivalve. Left valve more 

 convex than right. Hinge line long, straight, with one or two 

 small cardinal teeth and a lamellar lateral. Posterior ear wing- 

 like, longer than anterior. A byssal sinus present under right 

 anterior ear. Ligament in a groove, partly internal and partly 

 external. Posterior adductor scar large, subcentral ; anterior 

 scar absent in adults. Ordovicic-Recent. 



This rather inclusive genus is divided into very many subgenera 

 among which are Actinopteria, Pteronites, Ptychopteria and Monop- 

 teria. Many species are left here for want of better material to 

 determine their subgeneric relations. 



221. P. sulcata (Geinitz). (Fig. 585.) Carbonic. 



Fig. 585. Pteria sulcata. (Kansas Fig. 586. Pteria longa. (Kansas 



Pal., VI/II.) Pal., VI/II.) 



Marked anteriorly with two or three radiating furrows and with 

 several concentric folds. 

 Kansas, Nebraska. 



222. P. longa (Geinitz). (Fig. 586.) Carbonic and Permic. 

 Body of shell obliquely elongated and more or less arcuate. 

 Coal Measures of Interior. Permic : Oklahoma, Texas. 



223. P. petrosa (Conrad). (P. lingniformis E. and S.) 



Cretacic. 

 Surface marked only by concentric growth lines. 

 Ripleyan of New Jersey (Cliffwood-Wenonah). Montanan of 

 the Plains and of the Rocky Mountain region. 



