1912] The Glass Shrimps (Pasiphæa) in Northern Waters. H 



It is possible to distinguish Pasiphæa principalis and P multi- 

 dentata from another even in specimens which are so small that no 

 spines are developed on the pereiopods, by means of the shape of 

 the rostrum, of the scaphocerite and of the outer uropod. 



It is true that great changes take place during growth, but 

 still typical differences remain, which became evident to me while 

 examining a good number of young specimens from two localities 

 where the one or the other of the two species dominated, as far 

 as could be concluded from the adult. In the figs. 5, 6 and 7 are 

 reproduced camera drawings (an enlargement of 35 /i was used) from 

 six specimens, three tåken in deep water on the South Faroe Bank 

 and three in somewhat shallower water in. Sulen fiord, about 

 100 km. north of Bergen. 



From these drawings it will be seen that the two species may 

 be kept apart with certainty by means of the rostrum or the scapho- 

 cerite down to a size of 5 or 6 mm. (C), by means of the outer 

 uropod even at a size of 4 mm., lack of smaller specimens preventing 

 me from carrying the comparison further. These sizes of carapace 

 correspond to a total length of about 20, resp, 14 mm. and as the 

 larva of P multidentata, according to Bjorck (1911) leaves the 

 the egg when about 9 mm. long, it would appear to be possible 

 to distinguish this species from the other at almost every stage of 

 development. 



There is a marked correspondence in the shape of the scapho- 

 cerite and of the outer uropod, the thin portion of both these 

 appendages protruding more apically and the spine being shorter in 

 P. principalis than in P. multidentata. 



Kemp (1910, p. 42) seems to doubt the specific identity between 

 the European and American specimens of U P. princeps" still he 

 holds that the difference is only a racial one. An examination of 

 Smith's description (1884, p. 382 [38]) shows several points in 

 which they do not agree, arguing, I think, against applying the 

 same specific name to both. 



1. The eggs of Smith's species are very large, measuring 4 by 

 5 mm., while the eggs of the European species measure only 

 2 by 3 mm. 



2. The base of the 2nd pereiopod carries no spines in the 

 American species according to Smith's description, while all 

 the specimens of the present species longer than about 60 mm. 



