F. G. Percival—Punetation of Terebratulid Shells. 55 
The results are shown graphically in Figs. 1 and 2. It will be 
seen that the curve for 7. biplicata is a simple variation curve, 
confirming the fact that only one species was being dealt with, and 
incidentally supporting Davidson’s application of the name to a wide 
range of forms. The mode occurs at between 60 and 70 per square 
millimetre. The curve for Z. punctata shows a fairly pronounced 
hump a little beyond the mode, which lies between 110 and 130. 
Fie. 1. 
6 setae ae t s ae 
~ 50 .70 90 uo 13Q 450 170 190 210 230 250 
30 
20 
0 
30 40 50 60 70 60 90 100 “1a 120 (30 
Fie. 2. 
Fic. 1.—Curve showing variation in number of puncte per sq. mm. in 367 
individuals of J. punctata, Sby. Abscisses = puncte Be: sq. mm. 
Ordinates = numbers of individuals. 
Fic. 2.—Curve showing variation in number of puncte per sq. mm. in 166 
individuals of T. biplicata. 
