TANAIDACEA AND ISOPODA— TATTERSALL. 237 



elongate spoon. The oblique groove is very well marked. This interesting structure 

 has not been noted previously in this family of Isopods, but Barnard's figure of the 

 first pleopod of the male in Antarchirus kladophoros (1914, pi. XVIII B, pip. I) 

 makes it fairly obvious that a similar modification is present in that species, and his 

 figure of the same appendage in Neoarcturus oudops (1914, pi. XIX B, pip. I) suggests 

 a similar structure. I have found it in all the species of Antarcturus and Dolichiscus 

 in the present material. 



Ohlin (1901) has instituted the family Pseudidotheidae* for the species Pseudidothea 

 honnieri, Ohlin, entirely on the grounds of the modification of the first pleopods of the 

 male as accessory sexual organs. An examination of his figure shows a structure which 

 is in every way similar to that described above for the genus Antarcturus, the groove 

 on the lower surface of the exopod being well shown. It is a fact of considerable 

 interest that the same modification of the first pleopods of the male should be 

 developed in two distinct families. 



42. Antarcturus polaris (Hodgson). PL VIII, figs. 3, 4. 



Arctums polaris, Hodgson, 1902, p. 247, pi. XXXIV, fig. 2, pi. XXXV. 

 Antarcturus polaris, Richardson, 1913, p. 9. 



Occurrence. — Station 220, off Cape Adare, mouth of Robertson's Bay, 45-50 

 fathoms, bottom fauna, over seventy specimens, the largest male 43 mm., the largest 

 female 38 mm. 



Station 294, Ross Sea, 74° 25' S., 179° 3' E., 158 fathoms, bottom fauna, one adult 

 female, 33 mm. 



Station 314, 5 miles N. of Inaccessible Island, McMurdo Sound, 222-241 

 fathoms, bottom fauna, two males, 40 and 42 mm. 



Station 355, 77° 46' S., 166° 8' E., 300 fathoms, bottom fauna, one male, 36 mm., 

 sixteen immature. 



Station 356, off Granite Harbour, McMurdo Sound, 50 fathoms, bottom fauna, one 

 male, 28 mm. 



Remarks. — The essential spiny armature of this species can be seen in pi. VIII, 

 figs. 3 and 4, representing a young male, 20 mm. The fully grown specimens differ 

 from this figure only in the greater development of small spines or spiny tubercles on 

 different parts of the body, especially between and around the lateral and coxal spines 

 of the first four free thoracic somites and on the doi'sal and lateral surfaces of the 

 abdomen. These differences can be seen on a comparison of my figure with that given 

 by Hodgson. The large spines arming the body remain more or less constant in 

 position and number throughout life, but with the more robust form of the adult they 



* Collinge has doubted the validity of this family, and I was inclined to agree with him, but 

 Barnard (1920) has recently given further reasons for its maintenance. He has described a second 

 genus and species belonging to the family, Holidotea unicornis, which has the first pleopod of the male 

 modified in a similar manner to that here described. 



