THE OSTRACODA. 



263 



In addition to the numerous specimens of Stage I. there was a single female specimen 

 of (apparentl^r) Stage III. ; this with the aid of a slide-rule enables one to make an 

 empiric guess at the moan of Stage II. With a growth-factor of 1-6 for females it 

 appears tliat 12 X IQ = 1"92 ; 1-92 X 16 = 3-07 ; and wo may fairly presume that 

 the mean of Stase II. will bo a little more or less than 19 mm.*. 



It will be noticed that the curve of females at Stage I. shows a distinct double 

 hump, which can hardly be attributed to scarcity of specimens. 



Fig.C. 



CONCHCECIA ELEGAT^S, SarS. 



This species presents the same difficulty as some of the other small forms — namely, 

 of an overlapping of the curves in the male between Stages II. and III. ; some 

 specimens of I'O mm. were observed to have not yet developed secondary sexual 

 characters which were already shown by others at 09 mm. The same thing 

 appeared to be the case in the females at Stages IV.-in., III.-II., but their smaller 

 morphological differentiation renders it less obvious. 



As in rotundata (p. 273) and cnrta (p. 259), the differences in length between the 

 successive stages are so small that measurement to only one place of decimals does not 

 bring out clearly the boundaries between stages which are so noticeable in larger species, 

 such as magna. 



In consequence of these two unfavourable conditions, it is not possible to get really 

 satisfactory means for the various stages ; but, taking the means for female specimens 

 (compare fig. D, p. 264) of 11 and 1*2 mm., of 0-8 and 09 mm., and the median at 

 06, so as to eliminate the probable overlapping at I'O and 07 mm., we arrive at the series 

 0-6, 0-86, and 1-12. To this a fair approximation can be got by a growth-factor of 132 : 



• Since this was written, I have measured the two specimens of " lacerta" taken by the ' Research ' in the Faeroe 

 Channel (Proc. Zool. Soc. 1903, p. 122) and now in the British Museum. They were females of 2-0 mm. in length. 



