504 EEV. T. R. E. STEBBING ON CRUSTACEANS [May 22, 



Fam. Tbichoniscid^e. 



1898. TricJwniscidce, Sars, Crustacea of Norway, ii. p. 159. 



1900. TricJwniscidce, H. Richardson, Am. Nat. xxxiv. pp. 302, 306. 



In separating this family from the Ligiidae, Sars assigns to it the 

 genera TricJwniscus, TricJwniscoides, Haplophthalmus, ScypJiacella, 

 and Actonucus, while leaving to the Ligiidae the genera Ligia, 

 Ligidium, Titanetlies, Styloniscus, and StympJialus. In the latter 

 family the first antennae have the third joint minute, the second 

 maxillae have two plumose setae on the inner margin, the maxilli- 

 peds have the terminal part distinctly five-jointed, and the uropods 

 are described as freely projecting behind. In contradistinction to 

 this, in the Trichoniscidae the first antennae have the third joint 

 well developed, the second maxillae are without plumose setae on 

 the inner margin, the tnaxillipeds have the terminal part generally 

 imperfectly articulated, and the uropods have the peduncle broadly 

 expanded inside and partly covered by the last caudal segment. 

 There are other distinctions drawn by Sars, of more or less import- 

 ance, to one of which it is specially needful to call attention. In 

 the Ligiidae the second antennas have a "multiarticulate flagellum," 

 whereas in the Trichoniscidae they have a " flagellum composed of 

 only a restricted number of articulations." The restricted number 

 is not specified, but apparently it is not intended to exceed four or 

 five, or seven at most. Now both species included by Dana in his 

 genus Styloniscus at its institution have the multiarticulate fla- 

 gellum, which is " seven to ten-jointed " in magellanicus and " about 

 sixteen-jointed " in longistylis. But magellanicus by its maxillipeds 

 and character in general clearly belongs to Trichoniscus. There- 

 fore the distinction between the two families based on the number 

 of joints in the flagellum of the second antennae is no longer tenable. 

 That Styloniscus may still belong to the Ligiidae is possible. In the 

 Califoruian species gracilis, added to the genus by Dana in 1856, 

 the flagellum of the second antennae has about fourteen joints and 

 is nearly as long as the two preceding joints of the peduncle. The 

 peduncle of the uropods is distinguished from that of longistylis 

 by being scarcely twice as long as broad and on the outer side at 

 the middle becoming suddenly narrower. This recalls the corre- 

 sponding structure in Ligidium Jiypnorum. L T nluckily Dana could 

 not describe the rami because they were mutilated. He does not 

 describe the mouth-organs either in this species or in longistylis, 

 so that the genus remains obscure, covering two species which are 

 very doubtfully congeneric. Styloniscus gracilis is mentioned by 

 Stimpson in 1857, Budde-Lund in 1885, and Miss Harriet 

 Richardson in 1899 ; but they neither quote nor supplement the 

 meagre description given by Dana in the Pr. Ac. Philad. vol. vii. 

 p. 176. 



Sars makes the suggestion (Crustacea of Norway, vol. ii. p. 167) 

 that the genus Scyphacella of S. I. Smith may perhaps turn out 

 to Ip identical with Haplophthalmus of Schobl. A distinguishing 

 feature of Haplophthalmus is, however, as the name implies, that 



