268 



DE. G. H. FOWLEE— BISCATAN PLANKTON ; 



CONCHCECIA MAGNA, ClaUS. 



The actual measurements are as follows : — 



Stage I. 

 Mean, 3-36. 



Stage II. 

 Mean, 1-88. 



?. 

 4 

 26 

 26 

 <25 

 9 

 3 

 ^ 3 



1 

 17 

 40 

 54 

 64 

 16 

 5 

 1 



L 



stage III. I 

 Mean, 1'14. I 



r 25 



193 

 , 216 

 I 26 



mm. 

 3-6 

 3-5 

 3-4 

 3-3 

 3-2 

 31 

 3-0 

 2-9 

 2-8 



2-2 

 2-1 

 20 

 1-9 

 1-8 

 1-7 

 1-6 

 1-5 



1-4 

 1-3 

 1-2 

 1-1 

 1-0 



31 



23 I Stage I. 

 15 I Mean, 2-91. 

 22j 



f I Stage II. 

 40 ! ^^-"' ^■''■ 



1^ 



60 ! ^, TTT 



I Stage 111, 



^^^ i" Mean, 1-22. 

 17 1 



iJ 



Table J. — Total specimens measured: 754 ?+417(J=1171. 



Unusual features of this, the most plentiful species, are the flat-topped curve of 

 Stage I. in the females, and the double-humped curve of Stage I. in the males. These 

 features were consistently noticeable, when the observations were summarized from time 

 to time as the investigation proceeded, and appear to be genuine. There seem to be three 

 possible explanations of these abnormalities. The first (the most obvious) is that I have 

 confused together the successive stages of two parallel species with nearly identical 

 structure : this explanation does not commend itself to me (leaving out of count the 

 care taken over the work), because I do not believe that two such exactly similar species 

 can co-exist in such intimate association in the same locality ; this explanation must, 

 however, be borne in mind. A second possibility is that the larger " macrocheira " 

 forms may really belong to a different species from the smaller " magna " forms. This 

 would imply the very improbable result that of two closely-allied and intimately 

 associated species the one was represented only by Stage I.*, the other only by Stage II. 

 and perhaps smaller stages. 



* The observations recorded in the Systematic Part .seem to leave no doubt that the Halocypridae have two 

 stages with secondary sexual characters. 



