South African Crustacea. 65 



bottom, green sand. The Challenger specimen about 17 mm. long, 

 was taken off Cape Finisterre at a reputed depth of 1,125 fathoms. 



GEN. TEYPHOSA, Boeck. 



1871. Tryphosa, Boeck, Forh. Selsk. Christian., 1870, p. 117. 

 1906. Tryphosa, Stebbing, Das Tierreich, Amphipoda, pp. 68, 720. 



TRYPHOSA ONCONOTUS, n. sp. 

 Plate XXXV. 



There are two features of rather particular interest in this species 

 the dorsal hook on the fourth pleon segment, and the accessory lobe 

 on the branchial vesicles. The first of these may be compared with 

 the furcate dorsal process on the same segment in Pontoporeia 

 femorata, Kroyer, and with the arrangement in Guernea coalita 

 (Norman). Hansen, in his description of the adult female, shows that 

 the latter species is in fact provided with a sort of hook, the fourth 

 pleon segment having, behind the dorsal depression, a high rounded 

 carina, which is produced in front into a small rounded process. 

 In Aeanthoqammarus belkinii (Garjajeff) each of the first four 

 pleon segments has a dorsal process projected forwards.* The 

 suggestion may be ventured that in all these cases a facility is 

 provided for the male to hold the female firmly, in agreement with 

 the explanation of the modified sixth pair of side-plates in the 

 female of Mclita palmata (Montagu). The accessory lobe with 

 which the branchiae are provided in the new species is not perhaps 

 very unusual. Such a lobe is described and figured by Sars in the 

 Crustaces d'eau douce de Norvege for Gammaracanthus lacustris. 



Head with lateral angles acutely produced. Side-plates of peraeon 

 well developed, first not distally narrowed, first and second with 

 minute denticle at lower hind angle, fourth excavate behind. 

 Postero-lateral angles quadrate in second pleon segment, rounded 

 in first and third. Fourth pleon segment with deep dorsal depres- 

 sion followed by an upturned triangular process directed forward so 

 as sometimes to overlap the hind margin of the third segment. 



Eyes not perceptible. First antennae short, peduncle consisting 

 of one rather bulky joint followed by two small ones, flagellum 

 scarcely longer than peduncle, with nine joints, the first considerably 

 the largest ; accessory flagellum three-jointed. Second antennae not 



* In the Amphipoda Gammarideaot Das Tierreich, the name of Garjajeff's above- 

 mentioned species is erroneously given as balkirii. 



5 



