SCHIZOPOD, PSEODOMMA ROSEUM. 75 



Macropsis means the " long - eyed," the eyes being well 

 developed and perched on stalks which, comparatively, are of 

 a considerable length. On this occasion, however, I wish to 

 draw your attention to a Schizopod belonging to the same 

 family of the Mysidae, but in which the eyes are rudimentary. 

 I captured Pseudoinma roseum off Largs, 35 fathoms, bottom 

 mud. There was only one specimen (a female), and the tail 

 part of another. The majority of the Schizopoda are quick- 

 swimming creatures, small and fragile, and the method usually 

 adopted for their capture is by means of the tow-net. My 

 specimen was captured, however, by the shrimp trawl, and it 

 was while sifting the mud through the fine sieves that I dis- 

 covered this little treasure. 



P. roseum, when alive, is a striking and very beautiful little 

 creature, about half-an-inch in length, the colour being white, 

 streaked with brilliant carmine. The form of the body is 

 slender and nearly cylindrical throughout, the legs being very 

 slender and fragile. The telson is linguiform, broadest at the 

 base and tapering gradually towards the apex. My specimen 

 differs slightly from that described by Sars in having two more 

 terminal spines on the telson. This is, no doubt, merely a local 

 variation. 



The most striking characteristic, however, of this small 

 Crustacean is the rudimentary condition of the eyes, " forming 

 merely broad petaloid expansions of the ocular segment, partly 

 connate in the middle, and not exhibiting the slightest trace of 

 pigment or visual elements." According to Sars, however, there 

 is a ramification of the optic nerve within the ocular plates. 



These ocular plates occupy almost the whole breadth of the 

 frontal margin, being separated in the middle by a small cleft. 

 The outer edge is serrate. 



In the rough drawing accompanying this paper I have shown 

 the form and position of these ocular plates. As a comparison 

 of this species with a Schizopod possessing well-developed eyes 

 would be instructive, I have drawn underneath the head part 

 of Nyctiphanes norvegica, G. 0. Sars, which is abundant in the 

 deep water of the Firth of Clyde, showing its large and finely 

 developed eyes. 



So far as I am aware, P. roseum has not yet been recorded 



