OE DENISON UNIVERSITY 



73 



inch conglomerate above the quarry rock in the south Newark quarry. 

 It is here associated with A. veutricosa, Edtnondia sp. Sanguinolitcs 

 obliqiiiis, and Prothyrus ?neeki. 



The following measurements 

 this place : 



ustrate the range of variation at 



'}\o 



'^ 



tJ3 



•" r. 



<u '^3 •— 



•45--43 

 •47 --43 

 .51-.46 



•43-- 3 7 



Allorisma winchelli has once been found in shales above congl. I, 

 showing that it was continuous throughout the period during which 

 the free-stone was deposited. The animal lived buried in the mud, 

 and is found with the valves in connection oblique to the lamination, 

 and only in rocks which were originally mud of the shallow bays. 



■Allorisma vciitricosa, Meek. 

 (Plates VIII, Fig. 6: Cf Plate VII, Fig. i2>-) 



Our specimens differ considerably from Meek's descrijjtion and 

 also among themselves. The one figured expresses the extreme de- 

 velopment of the tendency of the species, being shorter and more 

 abruptly curved antero-ventrally and with more jjrominent beaks than 

 others. A well marked ridge marking off the antero-umbonal slope 

 is especially characteristic. 



Length 34 (24); height 29 (19); thickness iS (13); height at Yi 

 from posterior 22 (15}; thichness at same i)oint 13 (10); anterior wing 

 5; angle of postero-ventral margin with hinge line about 56°. Meas- 

 urements in parenthesis are of another specimen. 



