l86 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [BuU. 



degrees of reduction. Many of the SphEeromidae and Oniscoidea 

 such as Oniscus asellus and Armadillidium vulgare are capable 

 of rolhng the body completely into a ball. 



The head may be regarded as composed of seven coalesced 

 segments as in the Amphipoda, the segments being indicated by 

 the appendages. 



The eyes, which are always present in New England species, 

 are paired ; they may be small and simple, or large and compound, 

 made up of many ocelli. In the Tanaidae the eyes are situated 

 on stalks which are never movable, but in all other families the 

 eyes are sessile. 



There are always two pairs of antennae as in the Amphipoda, 

 but their relation to each other is somewhat different; for the 

 first pair, instead of arising dorsal to the second, arise nearer 

 the middle line and so may be designated as the inner antennae. 

 In the Oniscoidea the first pair are very small and inconspicuous 

 and are never more than three- jointed. Usually besides the three 

 joints of the peduncle there is a multiarticulate flagellum. In the 

 Idotheoidea the flagellum is uniarticulate, the segments evidently 

 being fused. In the Tanaidas the flagellum of the first antennae is 

 rudimentary or wanting in the females, as is also the case in the 

 female of Cyathura. 



The second antennae are usually composed of a peduncle of 

 five joints and a multiarticulate flagellum, but in Erichsonella 

 the flagellar joints are all fused to a single elongate tapering 

 joint. The flagellum is rudimentary in both sexes of the Tanaidae, 

 and in the genera Edotea and Cyathura. 



The mouth parts of the Isopoda resemble closely those of the 

 Amphipoda although there are a few important distinctive 

 characters, as for instance; in the Isopoda the first maxillae are 

 generally devoid of a palp while the second pair carry external 

 to the outer plate a lamellar appendage which is to be looked upon 

 as a palp; and the maxillipeds regularly have a single pair of 

 plates homologous with the inner plates of those of the Amphip- 

 oda, and external to the proximal segment there is an epipod or 

 epignath which is entirely lacking in that group. 



The mandibles usually bear a three- jointed palp but in the 

 Tanaidae, Oniscoidea, and Idotheidae the palp is entirely lacking. 

 The molar tubercle is wanting in the Cymothoidae, Limnoriidae, 

 Armadillididse, Oniscidae, and ^gidae. 



