THE NAUTILUS. 



VOJ,. XV. FEBRUARY, 19O2. No. 10. 



NOTES ON ASHMUNELLA. 



BY T. 1). A. (MMJKKRKl.L AND MAKY (.'<)(. I'KK. 



A large series of specimens from Manzanares Valley and Canon 

 Diablo, near Rowe, N. JM., shows that the A. thomsoniana type is 

 well divided into two races, to which the names thomsoniana and 

 porterce are applicable. The Manzanares Valley specimens are to 

 be designated portera;, although the basal tooth is in most cases 

 scarcely double, the inner denticle being reduced to a slight callosity. 

 The Canon Diablo form, coming from a somewhat higher altitude, 

 is referred to thomsoniana, although the basal tooth is often double as 

 in porterce. The fact is, that the character of the basal tooth, 

 whether double or single, is highly variable, and not to be relied on 

 to separate races. On the other hand, the size is much more dis- 

 tinctive. The following measurements of the greatest diameter 

 of the shell are worth giving: 



(1) A. thomsoniana from Canon Diablo. 9 are between 11 and 

 12 mm., 49 are 12, 52 are 12+, 53 are 13, 9 are 13 + , 1 is 14, and 

 1 is 14^ mm. 



(2) A. porterce from Manzanares Valley. 1 is 13+, 3 are 14, 13 

 are 14+, 16 are 15, 10 are 15 + , 5 are 16, 6 are 16+, 1 is 18 mm. 



(3) A. porterce from Beulah. 2 are 14, 12 are 14+, 17 are 15, 6 

 are 15+, 3 are 16 mm. 



If any one will take the trouble to plot out the curves from these 

 statistics, they will find that two and three are the same, with the 

 mode at 15, and the skew towards the smaller size. On ihe other 

 hand, one will be found to have an utterly different curve, with the 



