612 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XXH. 



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, 19OO. 



.(Type, Unio phaaeolnz Hildreth.) 

 Ptychobranchus 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; cavity of the beaks shallow; muscle scars rather deep. Animal 

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

 marsupiuin 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 orcrenulations, some- 

 times smooth; anal opening crenulate or smooth. 



t PTYCHOBRANCHUS PHASEOLUS Hildreth. 



* Unio phaseolus HILDRETH, Am. Jl. Sci., XIV. 1828, p. 283.' SAY, Am. Conch., 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., 1st ser.,111, 1845, p. 31, pi. ix, figs. 1-6. *CATLO\vand REEVK, 

 Conch. Norn., 1845, p. 62. *H. and A. ADAMS, Gen. Rec. 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., Ill, 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. xin, figs. 1, la, 16; * Manual, 1859, II, p. 

 137, fig. 659. 



* Unio planulata DESHAYES, An. sans A'ert., 3d ed., II, 1839, p. 672. 



* Uniofasciolaris CONRAD, New F. \V. Shells, 1834, p. 69. *FERUSSAC, Guer. Mag., 



1835, p. 27. * AGASSIZ, Arch, fur Naturg., I, 1852, p. 50. * CONRAD, Pr. Ac. 

 N. Sci. Phila., VI, 1853, p. 249. * KUSTER, Conch. Cab., 1861, p. 172, pi. LIV, 

 figs. 1-4. 



* Unio camelus LEA, 2 Tr. Am. Phil. Soc., V, 1834, p. 102, pi. xv, fig. 45; *Obs., I, 



1 Figure left out by the editor. 



3 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 ia worthy of a. 

 varietal name. 



