A REVIEW OF THE MYSIDACEA 157 



species, B. helgae, from very deep water off the west of Ireland was 

 known. It differs from the type species in the following characters : 

 (1) In the possession of very large eyes with normal functional visual 

 elements; (2) in the presence of a rostral plate; (3) in the longer and 

 more slender antennal scale; (4) in the form of the first and second 

 thoracic limbs and the more slender endopods of the third to the 

 eighth thoracic limbs ; (5) in minor details of the telson and remaining 

 appendages. It agrees closely with the type in the structure of the 

 mouth parts, especially in the form of the maxilla. It is a typical 

 member of the genus, the greatest difference, the form, structure, and 

 size of the eye, being obviously correlated with the shallower water in 

 which it lives, 120 to 264 fathoms, as against 447 to 720 fathoms for 

 B. helgae. 



Genus PSEUDOMYSIS G. O. Sars 



1'seudomysis G. O. Sars, 1879b, p. 430. 



PSEUDOMYSIS DACTYLOPS, new species 



Figure 59 



Description. — The typed are two adult females, not in very good 

 condition but sufficiently well preserved to make out the salient 

 characters. 



The species is very closely allied to P. abyssi G. O. Sars (1879b, p. 

 430), and it will be sufficient to point out the differences between 

 the two. P. dactylops differs from P. abyssi in the following 

 characters : 



(1) The rostrum (fig. 59, a) is considerably longer and more 

 pointed. It extends forward as far as the distal end of the first joint 

 of the antennular peduncle and is very acutely pointed. It far out- 

 reaches the eye. In P. abyssi the rostrum is shorter and extends for- 

 ward only about halfway along the first joint of the antennular ped- 

 uncle and to about the level of the eye. 



(2) The eyes (fig. 59, a) are pyriform and possess a long finger- 

 like process on the inner upper margin, which projects slightly beyond 

 the eye. The eyes are considerably larger than in P. abyssi, and the 

 visual elements, though reduced, are distinctly present and form a 

 corneal region to the eye. There is no pigment in preserved specimens. 

 In P. abyssi the eyes appear as a pair of small obtuse conical organs 

 with an acute conical projection at the distal end, but no fingerlike 

 process. 



(3) The telson (fig. 59, b) is relatively longer than in P. abyssi 

 though essentially of the same form and shape. It is almost twice as 

 long as broad at the base and is cleft for about one-third its length, 

 the cleft wide and triangular with diverging margins. Each margin 

 of the cleft is armed with about 30 sawlike teeth. Each lobe of the 



