REPORT ON THE CRUSTACEA MACRURA. 209 



the third pair of siagnopoda being uni-joiuted in the Astacidae, and two or more jointed 

 in the Stenopidse ; in the first pair of pereiopoda being the largest in the Astacidae, and 

 the smallest in the Stenopidae ; in the earpos being longer than the propodos in the 

 Stenopidae, and shorter in the Astacidae ; in the rhipidura being without a diaeresis in 

 the Stenopidae, thus corresponding with the Synaxidea, whereas in the Astacidae there is 

 always a diaeresis in the outer plates, and more or less indication of one in the telson. In 

 the Stenopidae the podobranchial plume is wanting in all the pereiopoda and in the 

 second pair of gnathopoda, the first pair alone having a branchial plume attached to the 

 mastigobranchia, and this is diminished in size. In the Astacidae the podobranchiae are 

 present, united with the mastigobranchial plate, from the first pair of gnathopoda to the 

 penultimate pereiopoda. 



In the Astacidae the ova are large and numerous, and the brephalos produced in 

 the Meo;alopa stage. In the Stenopidae the ova are very numerous and small, and 

 the brephalos produced in the Megalopa stage in Stenopus and in the Zoea stage in 

 Spongicola. 



Stenopus, Latreille. 



Stenopus, Latreille, Rigne anim. de Cuvier, ed. 2, vol. iv. p. 93. 

 ,, Desmarest, Consid. sur les Crust., p. 226. 

 „ Milne-Edwards, Hist. Nat. Crust., vol. ii. p. 406. 

 Dana, U.S. Explor. Exped., p. 601, 1852. 



Carapace furnished with a rostrum laterally compressed. 



First pair of antennae having two flagella. Second pair having a long, flat, and 

 obtusely pointed scaphocerite, the apex being continuous with the external margin. 

 Flagellum long and slender. Siagnos (or mandible) furnished with a three-jointed 

 synaphipod, of which the terminal joint is the longest. Third pair of siagnopoda 

 terminating in a small sharp dactylos. 



The first pair of gnathopoda short, six-jointed, furnished with a long basecphysis, 

 and the coxa supporting a small mastigobranchial plate, carrying a small, but well-formed 

 podobranchial plume. 



The second pair of gnathopoda long, slender, seven-jointed, supporting a small, 

 slender, uniarticulate basecphysis, the coxa supporting a rudimentary mastigobranchial 

 plate without any podobranchial plume. 



The anterior three pairs of pereiopoda chelate, the posterior being the longest and 

 largest. The first two pairs have the earpos longer than the propodos ; in the third 

 pair it is not quite so long. 



The posterior two pairs are slender, having the earpos very much longer than the 

 propodos, both of which are multiarticulate and terminate in a double-pointed dactylos. 

 All the pereiopoda support rudimentary mastigobranchiae without any podobranchial plume. 



(ZOOL. CHALL. EXP. PAP.T LII. 18S6.) *ff 27 



