256 Field Columbian Museum — Geology, Vol. III. 



Similarly on the lateral surface of the gular process the markings 

 fall into straight rows in which the pits of adjacent rows alternate 

 so as to form diagonal lines. Thus the pits are in regular rosettes — 

 patterns of six around one. In other parts of the plastron may be 

 occasionally recognized groups of fives, of fours and of threes, but 

 for the most part no regular arrangement is to be recognized. 



It is, therefore, probable that if the whole carapace and plas- 

 tron of B. variolosus and B. imbricatus were known the same regional 

 variation would be found to obtain. At all events, little reliance 

 can be placed upon the depth or arrangement of pittings as bases 

 for specific determination in this genus. 



MEASUREMENTS. 



M 



Length of carapace at median line 705 



Breadth of carapace 565 



Length of plastron 650 



Breadth of hypoplastra 480 



Length of bridge 360 



Greatest breadth of nuchal plate 145 



Least breadth of nuchal shield 007 



Greatest breadth of first pleural plate 112 



Greatest length of third pleural plate 205 



Greatest breadth of anterior pygal .1 70 



Breadth of entoplastron 148 



Thickness of epiplastra at gular eminence 060 



