NO. 1205. SYNOPSIS OF THE XAIADES SIMPSON. 783 



tQUADRULA PETRINA Gould. 



Unio petrinua GOULD, Pr. Boat. Soc. N. Hist., V, 1855, p. 228 ; * Otia Conch., 1862, 

 p. 218. * B. H. WRIGHT, Check List, 1888. 



* Margaron ( Unio) petrinua LEA, Syn., 1870, p. 55. 



Texas. Cragiu's localities, Verdigris and Neosho rivers, Kansas, are 

 probably erroneous. 



tQUADRULA AUREA Lea. 



* Unio aufeua LEA, Pr. Ac. N. Sci. Phila., Ill, 1859, p. 112; Ml. Ac. N. Sci. Phila., 



V, 1862, p. 195, pi. xxvi, fig. 264; * Obs., IX, 1863, p. 17, pi. xxvi, fig. 264. 

 * SOWERBY, Conch. Icon., XVI, 1868, pi. LXXXIII, fig. 438.* B. H. WRIGHT, 

 Check List, 1888. * P.KTEL, 'Conch. Sam., Ill, 1890, p. 145. 



* Margaron ( Unio) aitreus LKA, Syn., 1870, p. 37. 

 *Umo lolli CALL, Am. Naturalist, XV, 1881, p. 390.' 



Texas. 



tQUADRULA PAUPERCULA Lea. 



* I 'nio pauperculus LEA, Pr. Ac. N. Sci. Phila., V, 1861, p. 39 ; * Jl. Ac. N. Sci. Phila., 



V, 1862, p. 99, pi. xv, fig. 247 ; * Obs., VIII, 1862; p. 103, pi. xv, fig. 247.* B. H. 

 WRIGHT, Check List, 1888. 



* Margaron ( Unio) paupcrculus LEA, Syn., 1870, p. 55. a 



Texas. 



(Group of Quadrula infucata.) 



Shell small, rounded rhomboid, with a low, distinct posterior ridge, 

 truncated behind and angled back of the ligament; beaks moderately 

 elevated, subcentral; beak sculpture, four or five coarse, subparallel 

 ridges which curve upward behind, with fine, radial ridges between 

 them and the ligament; surface blackish, sculptured with zigzag or 

 chevron-shaped corrugations which often become pustulous below; 

 posterior slope having radial, broken wrinkles; pseudocardinals small, 

 stumpy; secondary lateral of the right valve present; beak cavities 

 moderately deep, slightly compressed; anterior scars small, smooth; 

 nacre rather dull, purplish. 



Animal with the marsupium occupying all four leaves of the gills; 

 inner gills the larger, free from the abdominal sac only part of their 

 length; anal opening without papillae. 3 



'An inflated form. 



2 Usually entirely free from sculpture excepting faint corrugations on the poste- 

 rior slope. A specimen belonging to Mr. William A. Marsh, from Village Creek, 

 Texas, shows slight tuberculation on the disks. 



3 I have been puzzled as to the relationship of this group and have been strongly 

 inclined to place it near chickasawhensis, but I now believe it is more closely allied 

 to the Pustulosa group. Its posterior truncation, the prominent angle behind the 

 ligament, and beak sculpture lead me to place it here. The general sculpture of 

 Q. peirina approaches that of these species. 



