Trichoniscoides albidus and T. sarsi. 85 



recorded the species as new to the Scottish fauna *. There 

 were no males in the few specimens I then took, but in April 

 of 1907 I came across a somewhat extensive colony of the 

 species, containing many males, at Gourock, on the Firth of 

 Clyde. A careful examination of some male specimens 

 showed some important differences in the structure of the 

 first and second pairs of pleopoda and the seventh peraeopod 

 as compared with the figures of these organs given by 

 Professor Gr. O. Sars in his great work l The Crustacea of 

 Norway ' f under the name of Trichoniscoides albidus 

 (Budde-Lund). 



Dr. Budde-Lund very kindly sent me the drawings he had 

 made of the first and second pairs of pleopoda of the male of 

 that species, and they virtually agreed with the structure of 

 these organs in the specimens I had under examination. 

 Moreover, both Canon Norman and Professor Sars were good 

 enough to send me Norwegian specimens of Trichoniscoides 

 for comparison with the Scottish examples. I dissected a 

 number of males, and found that the organs I have already 

 referred to had been most faithfully represented by Sars, and 

 these specimens were therefore specifically distinct from those 

 I had found in Scotland, which latter I have but little hesi- 

 tation in referring to Budde-Luud's species. I have therefore 

 the pleasure of naming the former T. sarsi, in compliment to 

 the distinguished Noi wegian carcinologist. 



The two species resemble each other in the general form 

 of the body, but differ in the following important points of 

 structure : — 



T. sarsi. T. allidus. 



First pair of pleopoda of male. 



The opercular plate is " large, 

 quadrangular, abruptly contracted 

 at the tip, and prolonged to a seti- 

 form ciliated lash curved outwards, 

 and accompanied inside by another 

 much smaller seta." The outer 

 lash is gracefully curved and is not 

 constricted at the middle. 



The outer corner of inner ramus 

 is only slightly produced and is 

 bluntly rounded at the tip. 



The opercular plate is broadly 

 triangular, the outside margin 

 being gently curved towards the 

 tip, which is prolonged to two seti- 

 form ciliated lashes of equal size. 

 Each lash is curved outwards, ia 

 constricted at about half it3 length, 

 and then abruptly bent downwards. 

 The outer margin is crenulated and 

 there springs a cilium from each 

 crenulation. 



The outer corner of inner plate is 

 greatly produced, being about £ of 

 the total length, and is acutely 

 rounded at the tip. 



* Glas. Nat, Hist. Soc. 25th June, 1907. 



t 'Crustacea of Norway,' Vol. ii. Iaopoda, pi. lxxiii. p. 165. 



