1912] The Glass Shrimps (Pasiphæa) in Northern Waters. 17 



in fact exist. Turning- first to the form of the rostrum, this feature 

 is very different in large individuals as shown by the outline clraw- 

 ings fig. 9, but there is less difference in young animals below 

 20 mm. (C) 1 ). These small individuals were determined as either 

 P. principalis or P tar da by means of the form of the scaphocerite 

 and the armament of the 2nd pereiopod. I suppose each set 

 belongs to the respective spedes merely because the specimens were 

 caught in areas where only one of the two forms is known to occur. 



The abdomen is comparatively larger in P. principalis, but as 

 will be seen from fig. 3, the ratio c 7a increases with age. This 

 latter faet seems not to have been noticed by Kemp, because I 

 think, most of his small specimens were in fact P. tarda. See 

 fig. 3. The rostrum which he figures as fig. 5, pl. IV, belongs 

 undoubtedly to that form. 



In the table on p. 16 I have collected together all the av ailable 

 data about the specimens of P. tarda examined by me. 



The depths within brackets are Soundings, and it may be 

 that the appliances were not towed actually on the bottom. As 

 mentioned before it appears from Kemps paper (1910) that P. tarda 

 also occurs SW of Ireland. 



Pasiphæa sivado Risso. 



This species is so characteristic that, so far as I am aware, it 

 has never been confounded with any other northern forms. It is 

 very rare in our waters. From the Kristianiafjord I have seen 4 

 specimens, C = 20, 19, 5 x /2 and 5 l / 2 mm. From the Langesunds- 

 fjord (on the East-coast) depth 200 m. one, C = 11 mm. Four 

 specimens, probably from Mosterhavn (N. of Stavanger) measure 

 (C) 7 Va, 7V2, 6 7 2 and 5 Vs mm. 



L ) C = length of carapace from ocular sinns to posterior edge. 



