95 



subcheliform structure. None of the forms belonging to the present group lead 

 a parasitic existence. The group contains as yet 5 families, all of which are re- 

 presented in the fauna of Norway. It is, however, very probable that it will be 

 found convenient to establish more families subsequently. 



Fam. 1. Asellidae. 



Characters. — Body more or less broad, depressed, with the lateral parts 

 of the segments lamellar. Cephalon of moderate size, without any rostrum, lateral 

 parts scarcely expanded. Caudal segment large, shield-like. Eyes, when present, 

 small, lateral. Both pairs of antenna? with multiarticulate flagella, the superior 

 ones much smaller than the inferior, and issuing close together. Oral parts nor- 

 mal. Legs ambulatory, except the 1st pair, which are distinctly subcheliform. 

 Pleopoda in female 4 pairs, the 1st being very small, not operculiform, consisting 

 each of a single rounded lamella; the 3 succeeding 25airs biramous, with both 

 rami lamelliform, outer lamella of 2nd pair very large and incrusted, so as to 

 form, together with the corresponding lamella of the other side, a sort of oper- 

 culum, completely covering the 2 succeeding pairs. Pleopoda in male 5 pairs, 

 an additional very small pair, constituting the copulative appendages, being inter- 

 posed between the 1st and 2nd. Uropocla comparatively large, biramous, with 

 the rami styliform or lamellar. 



Remarks. — In the restriction here adopted, this family is chiefly charac- 

 terized by the structure of the pleopoda, which differs considerably from that 

 found in the other Asellota. Whereas in these, the 1st pair in the female are 

 invariably transformed to a single large opercular plate, completely covering the 

 succeeding pairs, this pair, in the forms belonging to the present family, are of 

 inconsiderable size and not at all ojtercula'r, forming 2 discrete, simple, setiferous 

 lamella?. On the other hand, the outer plate of the 2nd pair is very large and 

 incrusted, lying in close contact with that of the other side, so as to obtect 

 completely the 2 succeeding pairs. In the male, there is found, immediately behind 

 the 1st pair of pleopoda, an additional pair of very small biramous appendages, 

 of which no trace can be detected in the female, and which represent the copulative 

 organs. As regards the other Asellota, the male operculum is apparently split into 

 3 juxtaposed segments, one narrow median segment, which exhibits a well-marked 



