ORTMANN: monograph of the naiades of PENNSYLVANIA. 57 



ROTUNDARIA TUBERCULATA (RafinCSqUc) (1820). 



Quadrula {Hotundaria) tuberculata (Rafinesque) Simpson, 1914, p. 903. 



Plate V, fig. 4. 

 Records from Pennsylvania: 



Marshall, 1895 (Allegheny River, Warren Co.). 



Rhoads, 1899 (Ohio River, Coraopolis, Allegheny Co., and Beaver, Reaver Co.; Beaver River, Wampum, 



Lawrence Co.). 

 Ortmann, 1909?), p. 201. 



Characters of the shell: Shell rather large and heavj-. Outline subrotund, or 

 ovate, or subquadrate, subtruncate, and sometimes slightly emarginate behind, 

 not veiy oblique, height and length not very different. Beaks moderately promi- 

 nent, inclined forward. Beak-sculpture consisting of numerous, fine, irregular, 

 broken, or wavy ridges, showing more or less distinctly a zig-zag arrangement, 

 with a posterior triangular loop most distinct, while anteriorly this arrangement 

 IS irregular. The first two or three Imrs are concentric, then follow three or four 

 which are only double-looped, and then other bars (even as many as ten or more), 

 which exhibit the iregular zig-zag sculpture. The beak-sculpture is continued 

 well upon the disc, and is immediately followed by the nodules of the latter. Shell 

 rather compressed, or only slightly swollen, disk gently convex, with an indistinct, 

 posterior ridge, which may be altogether absent. Posterior slope flat or somewhat 

 depressed, often with a more or less distinct wing-like expansion and elevated 

 posterior upper margin (chiefly in young specimens). Surface of shell covered 

 with tubercles or nodules, which, however, always leave free the anterior portion 

 (one-fourth to almost one-half) of the sheU. Tubercles verj^ variable in number, 

 size, arrangement, and shape; they may be rather few, or quite numerous, are 

 always quite irregular in size, and show no definite arrangement. GeneraUy 

 they are a little transverse, at least some of them. In the center of the sheU the 

 tubercles are generally most numerous, and upon the posterior slope and the wing, 

 they often assume the shape of radiating, nodulous ribs. In old shells the tubercles 

 disappear toward the lower margin, and in very large specimens the whole lower 

 half of the shell (or even more) may be without tubercles. 



Epidermis brown, lighter or darker, uniform in color, only in very rare cases 

 mere traces of broad greenish rays are barely indicated. Growth-rests slightly 

 darker, or not marked. 



Hinge-teeth strongly developed and ver>^ heavj'. Pseudocardinals large, 

 ragged, divergent. Verj' often there are one or even two subsidiary- pseudo- 

 cardinals in the right valve (one in front, the other behind the normal tooth). 



