ISOPODA 377 



3. Edotea Guerin. Second antennae of 4 to 6 segments and short; 

 abdomen composed of a single segment; legs prehensile: 3 species. 



E. triloba (Say) (Fig. 600). Length 7 mm.; width 3 mm.: New 

 Jersey to Maine; under stones and decaying algae, in muddy places 

 along the shore. 



4. Erichsonella Benedict. First antennae short; second antennae 

 long and composed of 6 segments; abdomen composed of a single seg- 

 ment; legs ambulatoiy: 3 American species. 



E. filifonnis (Say) (Fig. 601). Length 8 mm.; width 3 mm.: At- 

 lantic coast, south to Cape Cod ; in sand and among algae in shallow water. 



Family 9. ASELLIDAE.. 

 Body flattened, with 7 free thoracic segments, and with the ab- 

 dominal segments forming a single, shield-like plate; abdominal append- 

 ages exclusively branchial and numbering 4 or 5 pairs ; uropods terminal 

 and biramose: principally fresh-water animals; 17 American species. 



Key to the genera of Asellidae here described: 

 Oi Eyes present. 



&i Last 6 pairs of legs uniunguiculate 1. Asellub 



&2 Last 6 pairs of legs biunguiculate 2. Mancasellus 



Ca Eyes absent ; cave-dwellers 3. C^cidotea 



1. ASELLTJS Geoff roy. Abdomen about as broad as long; legs uniun- 

 guiculate; mandible with a palp: 7 American species; in fresh water. 



A. communis Say (Fig. 602). Length 15 mm.; breadth 5 mm.; first 

 antennae short, second long; first pair of legs prehensile and subehelate, 

 the others ambulatory, the last 3 being longer than the others: eastern 



United States; the commonest 



fresh-water isopod, occurring ^.^i^^^t^ ^^^^ipSSE^'^ ^^-^ . *o 



generally among vegetation. r^^^^S^^^ril 



2. Mancasellus Harger. ^- ------- -v^ 



Abdomen about as broad as 



lono" mandible without a naln* ^'^S- ^02 — Diagram of Asellus communis, 



lon^, manaiDie Witnout a paip, growing the internal organs (McMurrich). 



last 6 pairs of legs biun- J' second antenna- 2, first antenna ; 3, 



^ == brain ; 4, stomach ; 5, mandible ; 6, maxil- 



o-nipnlatp • fi «nppip« • in frp«li liped ; 7, nerve chord; 8, heart; 9, intes- 



guicuiare. o species, m iiesn tine ; 10, uropod ; ll, gills. 



water. 



M. macrourus Gannan. Length 12 mm. ; breadth 5 mm. ; first pair 

 of legs subehelate, the others ambulatory ; side of the head cleft near the 

 eye: central United States east of the Mississippi, often in caves. 



3. CffiCiDOTEA Packard. Body elongate and narrow; eyes wanting; 

 abdomen much longer than broad: 4 species; in caves and similar places. 



C. stygia Pack. Length 10 mm.; width 2 mm.; first pair of legs 

 prehensile, the hand being armed with 2 long and 3 short teeth: central 

 United States; in caves and deep wells. 



