COPEPODA 



147 



Ri of the maxillulae and the presence of a Se Re I pes I. The two genera are very nearly related, 

 but as the five species of Undeuchate form a very natural group I prefer to refer this species to 

 Chirudina. 



42. Chirudina abyssalis n. sp. 

 (PI. V figs 5 a— f; text-figs 40 a— c). 



Description. 1% Size of specimen from Thor St. 183 was 5-4 mm.; anterior division 4-3 mm.; 

 urosome n mm. 



The head is gradually rounded in front, without any crest; the rostrum is rather short, but 

 strong, directed downwards and slightly backwards (text-fig. 40 a). The cephalothorax, which is moder- 

 ately slender and slightly attenuated towards the front part as well as towards the end, is about 2-5 

 as long as wide; the first thoracic tergite is, at least dorsally, well separated from the head; the fifth 

 somite, which is well separated in front, 

 is laterally not produced, and has evenly 

 rounded corners (fig. 5 a). The anterior 

 division is about four times as long as the 

 abdomen. 



The genital somite, which is a 

 little wider than deep and as deep as long, 

 is in dorsal outline almost symmetrical; 

 the ventral surface is anteriorly rather 

 suddenly produced and posteriorly gradu- 

 ally sloping; the genital area is in ventral 

 view seen to be somewhat different from 

 that of the preceding species. The genital 

 somite possesses, dorsally, along hinder margin, short hairs, and ventrally tufts of longer hairs ; the fol- 

 lowing somites are more and less hairy, the hairs being longest dorsally and ventrally. The caudal 

 rami are about as long as wide; the terminal setae are distinctly shorter than the abdomen and about 

 three times as long as the Si. 



The antennulae extend to the end of the caudal rami; the measurements are very like those 

 of the preceding species. The exopodite of the antennae is r6 as long as the endopodite; the second 

 segment of the endopodite has 8 setae in \Ji and 7 in L,e; the first segment of the exopodite, which 

 is one third as long as the second, has inside a short protuberance with a short hair; the second seg- 

 ment has only a terminal seta. The mandibulae have, as shown in fig. 5 b, a rather characteristic shape, 

 and the maxillulae are completely like those of Ch. pustulifera. The maxillae (fig. 5 c) are only 

 slightly produced basally, and have the spinous areas on the hinder surface of the four proximal lobes 

 distinctly different from those of most species of Euchirella (cf. fig. 9 c!); in the first lobe a smooth area 

 is found surrounded by spines. The maxillipeds are scarcely different from those of the preceding species; 

 beyond the Si 3 in the third basipodite a longitudinal row of longer and shorter teeth is found (text- 

 fig. 40c); similar teeth were found in Ch. pustulifera, but not in Ch, Streetsii, 



19* 



Text-fig. 40. Chirudina abyssalis n. sp. 

 a. f 9. Head X 18. b. Pes T X 33- c. Maxillipes sin. Basp. Ill in post. 



view X 87. 



