960 THE AMERICAN NATURALIST.  [VOL. XXXIII. 
3 First pair of abdominal appendages of the males furciform, terminat- 
ing in two elongated nearly straight, acute tips. Third segment of 
third pair of legs of males hooked. (‘* Group IV ” of Faxon) 
C. lancifer, Miss., Ark. 
C. affinis, S. N. Y., Va., L Superior. . palmeri, Tenn., Ind. Terr. 
C. indianensis, S. Ind. . palmeri longimanus, Ind. Terr., 
C. sloanit, S. Ind., Ky. Tex. 
mississippiensis, Miss. 
Pak e 
C. propinguus, Dom. Can., Minn. C. longidigitus, Ark. 
C. propinguus obscurus, N, Y., Pa. C. dificilis, Ind. Terr., Ark. 
C. propinguus sanbornit, Ky., Ohio. C. meekiz, Ark. 
C. neglectus, Kan., Mo. C. erichsontanus, Tenn., Ala. 
C. harrisonii, Mo. C. alabamensis, N. Ala. 
C. virilis, Dom. Can., Tex, Kan. C. compressus, N. Ala. 
C. immunis, N. Y., Wy., Tex. C. medius, Mo. 
C. tmmunis spintrostris, Tenn., C. rusticus, Pa., la., Tex. 
Neb. C. spinosus, S. C., N. Ala. 
C. hylas, Mo. C. putnami, Ky., Ind. 
C. pilosus, Kan. C. forceps, N. Ala, Va, Tenn. 
C. nais, Kan. C. digueti, Mex. 
Third segment of second and third pairs of legs of males hooked. 
(* Group V ” of Faxon) 
C. montezume, Mex. C. montezume siea. Mex. 
C. montezume dugesii, Mex. C. Shufelditi, La. 
C. montezume areolatus, Mex. C. chapalanus, Mex. 
Astacus. —Last thoracic somite bearing a gill on each side, 
thus making eighteen gills (plus two or three rudiments) in 
each branchial chamber. Orifice of green gland on posterior 
face of tubercle. First abdominal appendages of males neither 
toothed nor bifid at the apex and none of the thoracic legs with 
hooks. Annulus ventralis represented by a transverse ridge. 
1 Margins of rostrum denticulate . ‘ : : ; : : F 
1 Margins of rostrum smoot : ; : : < 3 
2 Chelæ with a patch of soft setæ on outer sce ; . A. gambelli Gir. 
2 Chelæ naked on outer face : A. nigrescens Stimp. 
3 Postorbital ridges with a posterior spine or r tubercle ‘ a 
3 Postorbital ridges without a posterior spine or tubercle 
A. klamathensis Stimp. 
4 Acumen longer than distance between lateral teeth of rostrum 
: A. leniusculus Dana 
4 Acumen not longer than distance between lateral teeth of rostrum 
A. trowbridgii Stimp. 
