1912] 



The Glass Shrimps (Pasiphæa) in Xorthem Waters. 



9 



it is of restricted value because it is not found in small individuals 

 at all, and because it is inconstant in more advanced stages. The 

 first objection has not much weight, as it is a very common thing 

 for the young of very different species to resemble each other. 

 Regarding the second objection it is true that the number of spines 

 varies. but as shown by the table below, the limits of variation 

 do not touch each other as far as concerns P. multidentata on the 

 one hand and P. principalie and P. tarcla on the other, though 

 the two lastnamed can not be individually separated by means of 

 this characteristic, 



P. M 



ndtidentata 





P. 



principalis 





I 



. tarcla 





Size 



Spines 



Size 



Spine 



s 



Size 



Spines 



(C. mm.) 



Right 



Left 



(C. mm.) 



Eight 



Left 



(C mm.) 



Eight 



Left 



32 



12 



10 



52 



4 



5 



50 



3 



3 



30 



10 



9 



44 



3 



3 



49 



3 



2 



30 



12 



12 



42 



2 



2 



45 



3 



4 



30 



11 



12 



41 



3 



3 



40 



3 



3 



29 



7 



9 



41 



5 



5 



33 



1 



2 



29 



10 



12 



34 



3 



4 



33 



4 



4 



29 



12 



11 



33 



3 



3 



32 



1 



1 



27 



8 



9 



33 



2 



2 



31 



3 



3 



27 



10 



11 



32 



4 



5 



26 



2 



2 



26 



7 



8 



31 



2 



4 



26 



3 



4 



25 



9 



8 



31 



3 



4 



25 



3 



3 



21 



7 



8 



— 





— 



22 



3 



3 



Xnmber of spines on hase of 2nd perciopod of P. multidentata from the 

 Kristianiafjord, of P. principalis from the Færø Bank, and of P. tar da from the 

 Skagerack. 



Stephexsex also remarks that the form of the antennal plate 

 may cause difliculties. as he has seen a typical specimen of P. 

 multidentata whose right antennal plate is like that in P. prin- 

 cipalis I have had an opportunity of examining the same speci- 

 men. but failed to recognise the similarity. The scaphocerite in 

 question had a rather abnormal appearance. If such an isolated fact 

 had any significance at all it vvould perhaps point towards the 

 phylogenetic derivation of P. måltiden data from P. principalis or 

 a species closely allied to it. In a species of Sergestes I found the 

 left 3rd maxilliped closely resembling that of another distinct, though 

 nearly related species. 



