612 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



PTYCHOGEN-^E. 



Male and female shells essentially alike, embryos contained in dis- 

 tinct ovisacs with rounded bases, occupying the entire outer gills, 

 which, when gravid, consist of a series of folds. 



Genus PTYCHOBRANCHUS Simpson, 1900. 

 (Type, ZJwio j;/iaseoh(s Hildreth.) 

 PtycliolrancMis Simpson, Pr. Ac. N. Sci. Phila., 1900, p. 79. 



Shell triangular, solid, sometimes becoming arcuate in old specimens, 

 umbonal region rather elevated; beak sculpture consisting of faint, 

 somewhat broken ridges which have a tendency to be doubly looped; 

 posterior ridge rounded but well developed ; epidermis usually painted 

 with wavy hair line rays or broken, radiating bars, which show a tend- 

 ency to form square spots; hinge plate rather wide and flat; pseudo- 

 cardinals small, low, triangular and roughened; laterals club-shaped, 

 remote; cavityofthe beaks shallow; muscle scars rather deep. Animal 

 with inner gills free all or part of their length from the abdominal sac; 

 marsupium occupying the basal half of the whole length of the outer 

 gills and hanging in from six to twenty beautiful folds; ovisacs dis- 

 tinct, each ending below in an enlarged, rounded bulb which has a 

 colored spot in its center; mantle thin, with a dark, thickened border; 

 branchial opening large, with very minute papillae or crenulations, some- 

 times smooth; anal opening crenulate or smooth. 



t PTYCHOBRANCHUS PHASEOLUS Hildreth. 



* Unio phaseolus Hildketh, Am. Jl. Sci., XIV. 1828, p. 283.'— Say, Am. Concli., No. 



Ill, 1830, pi. XXII.— Short and Eaton, Transylvania JL, 1831, p. 77.— * Han- 

 ley, Test. Moll., 1842, p. 207 ; Biv. Shells, 1843, p. 207, pi. xx, fig. 50.— * Chenu, 

 Bib. Conch., Ist ser.. Ill, 1845, p. 31, pi. ix, figs. 1-6.—* CATLOWand Eeeve, 

 Conch. Nom., 1845, p. 62.— *H. and A. Adams, Gen. Eec. Moll., II, 1857, p. 491.— 

 ^SowERBY, Conch. Icon., XVI, 1868, pi. lxxiii, fig. 378.— *B. H. Wright, 

 Check List, 1888.— * P^etel, Conch. Sam., Ill, 1890, p. 163. 



* Margarita {Unio) phaseolus Lea, Syn.,1836, p. 38; 1838, p. 25. 



* Margaron ( Unio) phaseolus Lea, Syn., 1852, p. 38; 1870, p. 61. 



t * Unio planulatus Lea, Tr. Am. Phil. Soc, III, 1830, p. 431, pi. ix, fig. 13; * Obs., 

 I, 1834, p. 45, pi. IX, fig. 13.— *Deshayes, An. sans Vert., 2d ed., VI, 1835, p. 

 549.— * Chenu, 111. Conch,, 1858, pi. xiii, figs. 1, la, lb; * Manual, 1859, II, p. 

 137, fig. 659. 



* Unio planulata Desha yes. An. sans Vert., 3d ed., II, 1839, p. 672. 



* UniofasciolarisCoNnAD, New F. W. Shells, 1834, p. 69.—* Ferussac, Guar. Mag., 



1835, p. 27.— *Agassiz, Arch, fiir Naturg., I, 1852, p. 50.— * Conrad, Pr. Ac. 

 N. Sci. Phila., VI, 1853, p. 249.— * Kuster, Conch. Cab., 1861, p. 172, pL liv, 

 figs. 1-4. 



* Unio camelus Lea,^ Tr. Am. Phil. Soc, V, 1834, p. 102, pi. xv, fig. 45; *Obs., I, 



1 Figure left out by the editor. 



2 Typically this form is quite distinct from the ordinary manifestation of the spe- 

 cies, being very solid and much humped, but there seems to be every possible varia- 

 tion to the lighter, more compressed forms, and I do not think it is worthy of a 

 varietal name. 



