No.]:i05. Sl'SUrSIS OF THE XAIADES— SIMPSON. 703 



tUNIO PSORICUS Morelet. 



* Unio psoricus Morelet, Test. Nov., Pt. 2, 1851, p. 25.' — * Fischer aud Crosse, 



Miss. Sci., Pt. 7, II, 1894, p. 572, pi. LXi, fig. 2. 



Rio Usuinacinta, Guatemala. 



(Group of Unio gibbosns.) 



Shell solid, compressed or inflated, triangular ovate to elongate 

 ovate, arcuate when old, gibbons above, pointed or slightly biangulate 

 behind, with a moderate jjosterior ridge j beaks low, the sculjjture con- 

 sisting of a few very strong ridges which run parallel with the growth 

 lines; epidermis dull aud clothlike; pseudocardinals strong, rough; 

 laterals granular or vertically striated, club-shaped; beak cavities 

 very shallow; one or more slight furrows or ridges occur in the cavity 

 of the shell which run nearly parallel with the laterals; muscle scars 

 very deep and distinct. 



Marsupium occupying the entire outer gills; branchiae large, curved 

 below, inner the wider except at the posterior end, free from the 

 abdominal sac only part of their length; mantle very thin, with thick- 

 ened edges; branchial opening generally large. 



tUNIO GIBBOSUS Barnes. 



* Unio nasuia Lamarck,- An. sans Vert., VI, 1819, p. 75. — * Deshayes, An. sans 



Vert., 2d ed., VI, 1835, p. 538; 3d ed., II, 1839, p. 669. 

 *" Unio nasutus Agassiz, Arch, fiir Nat., I, 1852, p. 50. 



* Unio giUosus Barnes, Am. Jl. Sci., VI, 1823, p. 262, pi. xi, fig. 12.3—* jjil- 



DRETH, Am. Jl. Sci., XIV, 1828, p. 286.— Short aud Eaton, Transylvania 

 JL, 1831, p. 78.— ^^ Hanlet, Test. Moll., 1842, p. 207; Biv. Shells, 1843, p. 

 207, pi. XX, fig. 54.—* Catlow and Eeeve, Conch. Norn., 184.5, p. 59. — 

 *KusTER, Conch. Cab. Unio, 1852, p. 28, pi. iv, figs. 3, 4.— *H. and A. 

 Adams, Gen. Rec. Moll., II, 1857, p. 491.— ' Sowerby, Conch. Icon, XVI, 1868, 

 pi. Lxxiii, fig. 379.—* Calkins, Pr. Ottawa Ac. Sci., 1874, p. 42.—* Latchford, 

 Tr. Ottawa F. N. Club, 1882, p. 50.— *B. H. Wright, Check List, 1888.— 

 * P^TEL, Conch. Sam., Ill, 1890, p. 153.—* Baker, Moll. Chicago, 1898, p. 70, 

 pi. XIV, figs. 3, 4; XV, figs. 1-4. 



Margarita Unio gibhosus Lea, Syn., 1836, p. 38; 1838, p. 25. 



* Margaron {Unio) gihhosus LiiA, Syn. 1852, p. 38; 1870, p. 61. 



*Mya gibhosa Eaton, Zool. Text-Book, 1826, p. 220. 



* Unio mucronatus Barnes, Am. Jl. Sci., VI, 1823, p. 266, pi. xiii, fig. 13 (out- 



line). — * Agassiz, Arch, fiir Naturg., I, 1852, p. 50. 

 *lfi/a mucronata Eaton, Zool. Text-Book, 1826, p. 221. 



1 Probably another variety of semigranosus. 



2 This name vras given by Lamarck to the species under consideration before that 

 of Barnes, but Say had already used the name nasutus for a Unio, hence gibbosns 

 must be used. 



■''In 1820 Rafinesque bestowed the name Amblema gibbosa on someunionoidmollusk 

 which I can not determine. Since then Conrad in 1836, and others after him, have 

 used the specific name as of Rafinesque and apjDlied it to a Unio, which they have 

 figured and described. Barnes applied the name in 1823, properly characterizing it, 

 and it must stand, because at that time it had not been used in the genus Unio, 



