Weller — KinderhooJc Faunal Studies. 87 



is not distinctly shown in the type specimen, but it is believed 

 to be as shown in the illustration. In the original description 

 this wing is not mentioned, it not having been uncovered in 

 the type specimen at that time. The species was originally 

 described as Gervillia strigosa and it has since been referred to 

 the genus Pierinea, though it is much more oblique than any 

 other species referred to that genus. So far as its characters 

 are preserved, it seems to be cogeneric with the Coal Meas- 

 ure species Avicula longa, and it is therefore placed in the 

 genus Avicula although its hinge characters have not been 

 preserved. 



Pteronites whitei (Win.). 



Pi. III. f. 6-1. 



Avicula whitei. Bull. U. S. G. S. No. 153: 106. 



" Shell large, transverse, exceedingly oblique, with nearly 

 terminal beaks. Hinge-line more than three times the great- 

 est dorso-ventral dimensions. Anterior ear pouched, not dis- 

 tinctly divided from the body of the shell. Left valve ven- 

 tricose ; umbonal ridge somewhat arcuate, or nearly straight, 

 forming an angle of about 20° with the hinge-line ; slope 

 thence to the ventral margin very rapid — to the dorsal side 

 rather gradual and symmetrical to the very hinge-line — the 

 posterior wing not being divided from the body of the shell. 

 Ventral margin, in the middle rather straight and nearly par- 

 allel with the dorsal; posterior margin sigmoidal by a deep, 

 or rather shallow sinus, isolating the posterior end of the 

 cartilage plate from the body of the shell ; posterior wing tri- 

 angular, exceeding the shell. External surface marked by 

 numerous fine, irregular striae of growth. Right valve much 

 less ventricose, marked on the body and anterior slope by 

 numerous sharp, regular raised concentric striae which become 

 very faint posteriorly. Cardinal line in each valve with a 

 long, slender, bifid lateral tooth behind the beak." 



"Length of dorsal side, 53 mm.; greatest dorso-ventral 

 dimensions, 17| mm.; depth of left valve, 51 mm." 



Remarks. The specimens in the University of Michigan 

 collection which are labeled as types of this species are ten in 

 number, but of all these only two left valves approach perfec- 



