ORTMANN: monograph of the naiades of PENNSYLVANIA. 43 



Its absence in the Cumberland and iipi^er Tennessee is remarkable, but probably 

 accounted for by its ecological habits. On the Gulf plain, it is largely represented 

 by other allied species. 



^ Sterki says that the Lake Erie form is "little inflated and has few tubercles." 

 This fits the specimen before me, but I cannot judge from a single example whether 

 this is a constant difference. 



QuADRULA VERRUCOSA (Rafinesque) (1820). 

 Tritogonia tuberculata (Barnes) Simpson, 1914, p. 318; Tritogonia verrucosa 

 (Rafinesque) Vanatta, 1915, p. 554; Quadrula verrucosa (Rafinesque) 

 Utterback, 1916, p. 62. 



Plate IV, figs. 2, 3. 

 Records from Pennsylvania: * 



Rhoads, 1899 (Ohio River, Coraopolis, Allegheny Co., and Beaver River, Wanipuni, Lawence Co ) 

 Ortmann, 19096, p. 198. 



Characters of Shell: Shell large and heavy. Outline elongate-subtrapezoidal, 

 considerably longer than high. Beaks low. Beak-sculpture consisting of one or 

 two subconcentric bars, curving upwardly and nodular l)ehind, followed by addi- 

 tional bars, which are more or less distinctly double-looped, and break up into 

 nodules, which are indistinctly arranged in zig-zag waves. This sculpture is con- 

 tinued upon the disk. Shell moderately swollen or rather flat, with a distinct, 

 but narrow posterior ridge. In front of the latter the sides of the shell are flattened 

 or somewhat concave, thus forming a broad, shallow radial groove. The posterior 

 nodular part of the beak-sculpture is continued upon the posterior ridge as a row 

 of tubercles, which, however, are not very prominent, and gradually disappear. 

 In front of the posterior ridge the disk, including the groove, is thickly studded 

 with rather smaU, low tubercles, which are often more or less distinctly arranged 

 in diagonal rows, and represent the continuation of the beak-sculpture. Toward 

 the lower margin, these tubercles become irregular, and may disappear. Posterior 

 slope with ribs radiating from the posterior ridge; they are smafl, irregular, and 

 nodulous toward the beaks, but become larger toward the posterior end of the shell. 

 Epidermis yellowish to rusty brown and blackish, without distinct rays, but gen- 

 erally suffused with green in irregular patches. Often the whole surface is greenish, 

 and only the tubercles are more or less yellowish or brownish. Growth-rests more 

 or less distinct. Old shells are generally uniformly dark brown or blackish. 



Hinge-teeth well-developed, strong. Pseudocardinals divergent, large, ragged. 

 Interdentum moderately developed. Lateral teeth long, straight, rather heavy. 



