124 THE VOYAGE OF H.M.S. CHALLENGER. 



Neotanais, F. E. Beddard. 



Neotanais, F. E. Beddard, Proc. Zool. Soc. Lond., 1886, pt. i. p. 117. 



Definition. — Body elongated and narrow, everywhere of approximately the same 

 diameter. Cephalothorax slightly projecting between the antennae ; ocular lobes present 

 but extremely minute, oval, pointed anteriorly. First pair of antennae (in the male) 

 with a three-jointed peduncle and a flagellum of four joints. Second pair of antennae 

 more slender but of equal length, with a five-jointed peduncle and a short four-jointed 

 flagellum. Mandibles with the usual structure, with a slender extremity and a stoul 

 molar process. Chelae very stout, the distal section of the penultimate joint extremely 

 broad with a toothed margin anteriorly terminating in the usual slender hooked 

 extremity; last joint much more slender than the corresponding portion of the fifth 

 joint. Succeeding" thoracic appendages similar to each other, the first only somewhat 

 more slender and shorter than the rest. Abdominal appendages all present. Uropoda 

 extremely long, with an eight-jointed endopodite and a small two-jointed exopodite. 



Remarks. — I have thought it necessary to institute a new genus for two small 

 Tanaids, one dredged in the Atlantic off the coast of South America, in 1900 fathoms, 

 the other also in the Atlantic but further to the north, and in 1252 fathoms. This genus 

 comes nearest to Heterotanais, Sars, but differs in the great length of the endopodite of 

 the uropoda and in the fact that the chelae are fully developed and of the normal 

 structure in the male ; as in Heterotanais the exopodite of the uropoda is distinctly two- 

 jointed, and this character distinguishes both genera from Leptochelia, Dana, as also do 

 the form of the chelae in the male. A well-marked characteristic of this genus is the 

 specialisation of the thoracic appendages into an anterior and posterior series ; in the thn <■ 

 anterior thoracic ajapendages the distal joint is a simple, elongated, somewhat curved claw ; 

 in the posterior appendages this terminal joint is furnished at its extremity with a circlet 

 of stout spines and a long, mesially placed, slender hair. 



Neotanais americanus, F. E. Beddard (PI. XVI. figs. 4-6). 



Neotanais americanus, F. E. Beddard, Proc. Zool. Soc. Lond., 1886, pt. i. p. 118. 



The present species is the only representative of this new genus ; the specific 

 as well as the generic characters depend upon the examination of two male specimens, 

 each of which measures about 6 mm. in length. 



The body is depressed and elongated, everywhere of approximately the same diameter. 

 It is smooth both dorsally and ventrally, with no hairs or spines. 



The cephalothorax is pear-shaped, narrower anteriorly and wider posteriorly ; it is 

 about as long as the first two segments of the thorax taken together ; the anterior margin 



