724 



CRUSTACEA. 



Family ONISCID^. 

 Subfamily ONISCLN^l. 



The OniscinoB are the " Porcellionides" of Edwards. The distinc- 

 tions of this group have been well drawn out by this author. We 

 add only a few remarks on the antennae. A characteristic feature 

 of these organs, as regards position, is the fact, that they are geni- 

 culated at the fifth articulation as well as near the head, which gives 

 them two abrupt flexures, somewhat like the form of the letter Z. 

 The flagellum consists of one to three oblong joints, besides (as appears 

 not to have been noticed) two or three small apical joints. Of the for- 

 mer there are commonly but two ; and when there are three, it arises 

 from a subdivision of the first of these two. This was evident to us 

 in a species of Scyphax, which, though not correctly one of the Onis- 

 cinse, is similar in its antennae : in specimens three to three and a 

 half lines long, the flagellum was two-jointed, with the first joint the 

 longer ; while, in specimens four to four and a half lines long, the 

 flagellum was three-jointed, and the first articulation was fainter than 

 the second, and plainly cut across the first of the two joints in the 

 two-jointed flagellum. The joints at the extremity are either two or 

 three in number ; the last is slender and somewhat spiniform or sub- 

 cylindrical, with a few setules at apex ; the other one or two are quite 

 short, and the articulations sometimes are not very distinct. These 

 parts are illustrated in our figures on Plates 47 and 48. The surface of 

 the antennary joints is usually thick set with very short hairs, or 

 more sparsely with spines. In the genus Deto, the flagellum of the 

 antennae is said to have four joints ; whether this includes the last of 

 these small terminal joints or not, we cannot say from observation. 

 It is possibly so, as all the joints of the flagellum are very short. 



From the occurrence of both two and three-jointed flagella, in diffe- 

 rent specimens of the same species that are so nearly of the same size, 

 as in the Scyphax, alluded to above, it is apparent that the distinction 

 as to number of joints cannot be a generic characteristic, and at the 

 most would separate only subgenera. It is on this account, added to 

 other points of identity, that we have not retained Porcellio, Oniscus, 



