714 



CRUSTACEA. 



caudales ultra abdomen non exsertae, lamellatae. Mandibulae non 

 palpigerae. Antennae internae inconspicuae. 



Fam. II. Oxiscma:. — Corpus saepius minus convexum, vel stricte vel 

 laxe articulatum. Abdomen multiarticulatum, segmento ultimo 

 parvo. Appendices caudales bene exsertae, styliformes. Mandi- 

 bulae non palpigerae. Antennae internae inconspicuae. 



Fam. III. Asellidje. — Corpus saepius valde depressum et laxe articu- 

 latum. Abdomen 1-6-articulatum, segmento ultimo magno, scutel- 

 lato. Appendices caudales styliformes, raro obsoletae. Mandibulae 

 palpigerae. Antennae internae conspicuae. 



The Asellidae correspond to the " Isopodes Asellotes" of Edwards, 

 excepting that we exclude his " Asellotes Heteropodes," which are 

 Anisopoda. The Oniscidae include the "Cloportides Maritimes" of 

 this distinguished author, together with part of the "Cloportides 

 terrestres," viz., the " Porcellioniens ;" while the Armadillidae comprise 

 the remainder of the " Cloportides terrestres." 



The Armadillidae and Oniscidae appear to rank before the Asellidae. 

 This is to be inferred from the fact, that the former are mostly terres- 

 trial, while the latter are aquatic ; for the principle which Agassiz 

 has brought forward appears to be of very general application, that in 

 a given group, the terrestrial species are highest in organization. 

 Moreover, the loose structure of the Asellidae seems to be proof of 

 inferiority to the well-formed, compact, and symmetrical Armadillo 

 and Oniscus. The antennae of the Asellidae also are more largely 

 developed, and the caudal stylets are usually longer and more projecting 

 than in the Armadillidae and most Oniscidae, giving farther evidence of 

 vegetative elongation in either direction, at the expense of concen- 

 tration. These reasons may not be of great weight, yet they seem, 

 in the doubtful state of the case, to point to the conclusion here 

 adopted. 



The following are the known genera of living species, and the sub- 

 families into which they are naturally grouped. 



