﻿340 PTYCHOBRANCHUS 



pseudocardinals, a narrow, curved hinge plate, and two lieavy, 

 club-shaped laterals ; right valve with one pseudocardinal and 

 one lateral ; hcak caxilies shallow ; nnisele scars w ell impressed ; 

 nacre 1 luish to Hesh-color or yellowish. The male shell is 

 somewhat arcuate when old and is generally rounded behind ; 

 that of the female has the basal region slightly produced and 

 the rounded posterior point raised a little above the base line. 

 Length (male) no, height 58, diam. 35 mm. 

 Length (male) 75, height 35, diam. 23 mm. 

 Length (female) 82, height 40, diam. 25 mm. 

 Tennessee and Cumberland River systems. 

 Type locality. North Fork of the Ilolston River. 

 Unio siibtnitiis Sw, Jl. Ac. Sci. Phila., \', 1825, p. 130; Am. 

 Conch., 1, No. 2, 1831, pi. XV. — Conr.\i), Am. Jl. Sci., XXVI, 

 1834, p. 343, pi. I, fig. I ; Monog., X, 1838, p. 85, pi. xlviii. 

 fig. 1.— Hani.ky, Biv. Shells, 1843, p. 176, pi. xx, fig. 34. — 

 Chenu, Bib. Conch., ist ser., IH, 1845, p. 25, pi. iv, figs. 2, 

 2a, 2b. — KusTER. Conch. Cab. Unio, 1856, p. 164, pi. xlvii, 

 fig. 4. — SowRRBY, Conch. Icon., XVL 1868, pi. lxxii, fig. 



Mav'^arita (Unio) suhtcntus Lea. Syn., 1836, p. 13; 1838, p. 14. 

 Margaron (Unio) suhtcntus LiJA, Syn., 1852, p. 21 ; 1870, p. ^2. 

 Medionidus suhtcntus Simpson, Syn., 1900, p. 591. 

 Ptychohranchus suhtcntus Ortmann, Ann. Car. Mus., VII I, 



19 1 2, p. 308, fig. 15. 

 Unio suhtcnta Desiiayes. An. sans Vert., 2d ed., Yl, 1835, p. 



555- 



Ortmann, (1. c. ) , has recently shown that this species is a 

 Ptycliohranchus and not a Medionidus. 



\ ESCHATIGEN.^.. 



Male and female shells alike ; embryos in distinct, short ovi- 

 sacs forming a border to the entire outer gills. 



