1902.] NATURAL SCIENCES OF PHILADELPHIA. '^l'^ 



as P. lordi, collected by Mr. C. H. T. Townseud in the Organ 

 mountains, N. M. It was found that these differed materially from 

 one another and from P. rhomboidea, and also from P. gyrma as 



Number of 

 specimens. 

 60 



Number of 

 specimens. 



ISO 



1.3 1.4 1.5 1.0 1.' 1-8 1-y -•" 



,, , „ Ratio of lenffth to breadth (average 



Ratio of length to breadth (average ^^^^^Jj^^ies 1.8). 



of whole series 1.0). rhomboidea, Gallinas river (re- 



P. humerosa, Arroyo Pecos (fossil). ^ 445 specimens. 



145 specimens. 



^ Frequency polygons. 



Fig.l. 

 figured by F. C Baker. The following table indicates the nature 

 of the differences : 

 Lateral teeth witi, .lentklcs of two Au.. Umg ones alternating with 



LatemM^th will.' long -k""^'!-. n,„ obvionslyof two .i,.., . 2 



