238 REiPORT OF NEW JERSEY STATE MUSEUM. 



Pleopoda in female in four pairs, first very small, not operculi- 

 form, consisting each of single rounded lamella. Three succeed- 

 ing pairs biramous, with both rami lamelliform, outer lamella 

 of second pair very large and incrusted, and forming together 

 with corresponding lamella of other side sort of operculum, com- 

 pletely covering two succeeding pairs. Pleopoda in male of five 

 pairs, an additional very small pair, forming copulative append- 

 ages, interposed between first and second. Uropoda compara- 

 tively large, biramous, rami styliform or lamellar. 



Genera about four, and most of them entirely fresh-water in 

 habitat. 



Genus ASELLUS G. St. Hilaire. 

 The As els. 



Asellus G. St. Hilaire, Hist. Insect., H, 1764, p. 671. (Type Oniscus aquaticus 



Linnaeus, monotypic, though species polynomial.) 

 F Lirceus Rafinesque, Annals of Nature, 1820, p. 7. Type Lirceus fontinalis 



Rafinesque, monotypic. 

 Abacura S. F. Baird, Iconographic Encyclop., H, 1851, p. 112. Type Asellus 



covimimis Say, monotypic. 



Body broad, depressed, with lateral parts of segments simple, 

 not laciniate. Cephalon not very large, rounded, truncated in 

 front, lateral faces convex. Caudal segment very broad, slightly 

 produced at tip. Eyes, if present, very small, consist of limited 

 number of usual elements. Superior antenuce scarcely longer 

 than peduncle of inferior ones, latter slender, elongated, without 

 any outer appendage on peduncle. Mandibles with well-de- 

 veloped palp, molar expansion thick, subcylindric in form. 

 Second pair of maxillae with outer lamellae broad, laminae edged 

 with numerous curved and coarsely denticulated spines. Max- 

 illipeds, in female, at base with posteriorly pointing setous 

 lappet, epignath broad, edged with bristles. First pair of legs 

 with carpus very small, propodus much larger and broader in 

 male than in female. Succeeding pairs rapidly increase in length, 

 carpal joint well developed, propodal one linear, dactylus spinu- 

 lose inside. Uropoda with subequal rami, slender, styliform. 



A single species in our limits, common throughout our fresh 

 waters. 



