TANAIDACEA AND ISOPODA— TATTERSALL. 2^5 



maxillae and maxillipeds. As to the first of these, Collinge's statement is based on 

 Hodgson's figure, and I find the difl'erence in this respect not so great in actuality and 

 negligible from a specific point of view. 



With regard to the maxillae, CoUinge states that there are eleven spines on the 

 outer lobe of the first pair in G. antarcticus, and only eight (or nine) in G. acutus 

 according to Hodgson. It has not been possible for me to examine all my specimens 

 with regard to this character, but in one specimen of G. acutus I found eight spines on 

 the outer lobe of the first maxilla, and in another specimen ten spines, so that the 

 number would appear to be subject to some variation. 



One other difference may be mentioned for what it is worth. Pfeffer figures the 

 appendix masculina on the second pleopod of the male of G. antarcticus as extending 

 backwards to the level of the end of the rami of the third pleopods. The only adult 

 male of this species available in the material at my command agrees with Pfefter's 

 figure in this respect. In the two adult males of G. acutus in this collection the 

 appendix masculina on the second pleopod is relatively much longer, and extends 

 as far backwards as the tip of the outer branch of the uropods. 



It may here be noticed that G. acutus appears to mature later than G. antarcticus, 

 and eventually to reach a larger size. In a male G. antarcticus of 52 mm. the penial 

 appendages on the sternum of the first abdominal somite are present, but there is no 

 appendix masculina on the pleopods. A male measuring 58 mm. is fully adult in both 

 respects. A male specimen of G. acutus, 62 mm., is still without the appendix 

 masculina on the second pleopods. Unfortunately, I have no males between this 

 size and 92 mm., so that I am unable to say at what size it really becomes fully 

 mature. 



My largest specimen of G. antarcticus is an adult female measuring 59 mm. 

 PfefFer's longest specimen was 62 mm., but CoUinge gives the length of his largest 

 specimens as 88 mm. On the other hand, the largest specimen of G. acutus in this 

 collection is 99 mm. Hodgson gives the maximum length of his specimens as 119 mm.; 

 30 mm. larger than the biggest G. antarcticus yet recorded. 



As Tait (1917) has already noted, G. antarcticus is a shallow water form. The 

 " Scotia " specimens were invariably taken in water of less than 12 fathoms, while the 

 specimens in the present collection are from depths of less than 15 fathoms. On the 

 other hand, Richardson records G. acutus from the shore to 38 fathoms ; the " Scotia " 

 collected it in 161 fathoms ; Hodgson gives the depth as 20-125 fathoms ; Vanhoffen 

 examined a single specimen from 208 fathoms ; while the specimens I have examined 

 were obtained in depths varying from 45-300 fathoms. 



As a result of these considerations I think that we can best express the relationships 

 of these two forms by regarding G. acutus as a variety of G. antarcticus, inhabiting 

 colder and deeper water, growing to a somewhat larger size and maturing later, and 

 distinguished in general form by its less robust proportions, slenderer legs and more 

 pointed apex to the metasome. It is in that Hght that I have regarded it here. 



