262 



DR. a. H. FOWLER — BTSCATAN PLANKTOIST : 



.Tudgina: by the lens^tlis recorded, Dr. Miiller seems to have measured a "length over 

 all," from the tip of the rostrum to the tip of the posterior spine. This was not adopted, 

 firstly, because both spine and rostrum are often broken or bent ; secondly, because, as 

 they appear to be disproportionately longer in the older stages, they would probably 

 not give a true standard of comparative growth at different stages ; thirdly, because 

 the measurement over all would not be comparable with those made in the other 

 species, where the " length " is from the projection of the anterior border below the 

 antennal incision, backwards, parallel to the dorsal border. Portunately, it is generally 

 easy to open and turn back the left shell in daphnoldps, without serious distortion; this 

 having been done, the base of the on the micrometer-ocular scale was laid carefully to 

 the most prominent point on the anterior border of the left shell, the scale laid as 

 closely parallel as possible to the dorsal border ; the point where the posterior curve 

 upwards to the spine intersected the base-line of the scale was then read as the 

 " length." This reading seemed to be at any rate comparable with that taken in other 

 species ; but the experimental error is perhaps rather greater in daphnoides, as the 

 posterior cvirve probably varies in radius to some extent. While therefore the individual 

 measurements are perhaps less accurate than in the other larger species, they are, 

 doubtless, sufficiently so to give a reliable mean, owing to their number. 



Judging by the analogy of more plentiful species, there can be little doubt that 

 daplinoides var. minor, Miiller {==lacerta, Brady & Norman), is the penultimate stage of 

 daphnoides var. typica, Miiller, that is to say, the lower stage with secondary sexual 

 characters. Unfortunately this stage was not represented in the Biscayan collections, 

 but a rough measurement of MiUler's figure (xxxi. 1) yields a length of about 1"8, 

 measured by my method. A few specimens of var. typica were measured by both 

 methods, but no relation appeared between the two sets of figui'es *. 



The actual measurements were as follows : — 



Stage I. 

 Mean, .3-08. 



1 



5 



41 



15 



.31 



Stage III. 



mm. 

 3-5 

 3-4. 

 3-3 

 3-2 

 31 

 3-0 

 2-9 

 2-8 

 2-7 

 2-6 

 2-5 

 2-4 

 2-3 

 2-2 

 1-2 



Jl 

 24 



48 



Stage I. 



Mean, 2-34. 



5 J 



Table E.— Total specimens measured : 112 ? -I- 88 ^ = 200. 



From tip of rostrum to tip of spiae they varied from 5-0 to 5-5 mm. 



