HCHIZOPODA. 35 



Pleopods. — The lateral lobe is less developed in ]\[. farrani tliau in M posthon. 



Telson. — In M. farrani the cleft is armed with only about thirteen spines, 

 whereas in M. posthon there are about thirty-six. In the former, moreover, the lateral 

 margins of the telson are armed with not more than twenty-six spines, not arranged in 

 series, and situated only on the distal two-thirds of the margin. In 31. posthon the 

 lateral margins are armed throughout the entire length with about seventy spines, 

 arranged, at any rate, distally in series. The whole telson in M. farrani is more 

 slender than in M. posthon. 



The spines on the inner uropods of M. posthon appear to be somewhat longer than 

 in A[. farrani. I have already expressed the opinion that the genus MetamysideUa of 

 Illig is synonymous with Afi/sidetcs. The type species of the former, ^1/. kerguelensis, 

 Illig (1906), is, however, a much smaller species than M. posthon, measuring only 

 10 mm. in length. It is otherwise closely allied to the latter, but differs iu having 

 the antennular peduncle almost equal in length to the anteuual scale and in the details 

 of the armature of the telson. 



\i Mysidopsis incisa, G. 0. Sars (1885), should iu future Ije found referable to the 

 genus Mysidetes, as seems probable, it differs from the present species in size, iu 

 having fewer joints in the tarsus of the thoracic limbs, and in the details of the 

 armature of the telson. 



I should mention here that I do not attach too great an importance to the 

 difference in size between M. kerguelensis and Mysidopsis incisa as compared witli 

 31. posthon as a .specific character, for I have found both males and females of 

 31 farrani quite sexually mature at 15 mm. (judging from the characters of the 

 antennular bru.sh in the male and the incubatory lamellas in the female), while the 

 species, fully grown, reaches to 28 mm. in total length. 



Sub-Family Mysin.^. 

 Gbnus Antarctomy'si.s, Coutiere. 



Mijsis, Holt ami Tattersall, I'.XiC, (1). 

 Antarctomi/sis, Coutiere, lOoii. 



This genus has lieen recently established by Coutiere for the reception of the 

 species Itrieffy noted as 3fysis mH.vinut, Hansen (MS.), in tlie preliminary notice of 

 this collection. 



There can be little doubt as to the correctness of the reasons which have led to its 

 formation, since the Ijiramous character of the fifth pair of pleopods in the male offers a 

 character of undoubted generic value, as distinguishing 3Iysis 'maxima from the genus 

 3Iysis [sens, stricto). The genus Jlemimysis has the fifth pair of pleopods in the male 

 biramous and natatory, but the third pair are only imperfectly l)iramous, the outer 

 ramus being very minute and single-jointed, whereas in Antarctomysis the tliird pair 

 resemble the fifth iu having both rami multiarticulate and setose. 



