NO. 1205. SYNOPSIS OF THE XAIADES— SIMPSON. 579 



Beak cavities shallow; dorsal scars numerous, exteuding from the cav- 

 ity downward and forward. Anterior muscle scars three, distinct, pos- 

 terior large, indistinct; front end of the shell usually thickened; a row 

 of plications often occurring just below the laterals, as in Cristaria. 

 Animal unknown. 



(Group of Hyriopsis Malatus.) 



Shell somewhat trapezoidal, with a posterior ridge, biangulate behind, 

 with a very high, pointed, triangular, posterior wing, and a smaller, 

 pointed one in front, which projects forward; beaks low, sculpture not 

 seen; epidermis brown; pseudocardinals broken up into denticles; 

 hinge line slightly curved; the three anterior muscle scars separate and 

 deep; dorsal scars not extending greatly downward in front; nacre 

 bluish white. 



t HYRIOPSIS BIALATUS Simpson.^ 



*Unio delphinus Gruner Arch, fiir Naturg, 1,1841, p. 276, pi. ix, ligs. 1, la-c. — 

 *Delessert, Rec. Coq. Lam., 1841, pi. xix. fig. 3, 3«, 3&.— *Lea, Tr, Am. Phil. 

 Soc, VIII, 1843, p. 218, pi. xvii, fig. 35; * Obs., Ill, 1842, p. 56, pi. xvii, 

 fig. 35.*—* Kuster, Conch. Cab. Uuio, 1852, p. 18, pi. ii, figs. 2-4. — *Hanley, 

 Biv. Shells, 1856, p. 381, pi. xx, fig. 44.—^ H. and A. Adams, Gen. Eec. Moll., 11, 

 1857, p. 498.— *Chenu, Man., 1859, II, p. 143, fig. 707.— Soaverby, Conch. Icon., 

 XVI, 1866, pi. XLiii, fig. 238.— *MoRELET, Series Couch., IV, 1875, p. 345.— 

 ■ P^TEL, Couch. Sam., Ill, 1890, p. 150. 



■' Margaron ( TJnio) delphinus Lea, Syu. 1852, p. 19 ; 1870, p. 28. 



""Unto megapients More'let, J. de Couch., XII, 1863, p. 159. — *' P^tel, Conch. 

 Sam., Ill, 1890, p. 158. 



Southeastern Asia, including Cambodia, Siam, and the Malay Penin- 

 sula. 



(Group of Hyriopsis cunmigii.) 



Shell rather thin, with a high wing posteriorly, and a smaller one in 

 front; beaks greatly compressed, their sculpture at first consisting of 

 fine and later of coarse concentric ridges, extending well on to the 

 disk; corrugations on the posterior sloj^e distinct. 



HYRIOPSIS CUMINGII Lea. 



Tlnio cwmingii Lea, Pr. Ac, N. Sci. Phila., VII, 1852, p. 54.— * Lea, Jl. Ac. 



N. Sci. Phila., I v, 1860, p. 240, pi. xxxv, fig. 120; * Obs., VII, 1860, p. 58, pi. 



XXXV, fig. 120.— -^H. and A. Adams, Gen. Rec. Moll., II, 1857, p. 498.— 



*Sowerby, Conch. Icon., XVI, 1866, pi. xlix, fig. 264.— *Heude, Conch. 



Fluv. Nank., VIII, pi. lxiv. 

 * Margaron ( Unto) eumingii Lea, Syu., 1852, p. 19 ; 1870, p. 28. 



China. 



'I regret that Gruuer's well-known name deljjliinns was previously used for a Unto 

 by Spengler, and the term megapterus of Morelet was applied by Rafiuesque to a 

 Mei apt era {Unto) anA. used by Chenu under the generic name H/io before 1863. It 

 will therefore have to have a new name. 



-Lea described this 8])ecie8 under tlio above name, not knowing that it had been 

 already applied to the same species l)y Gruner. 



