ORTMANN: monograph of the naiades of PENNSYLVANIA. 19 



crossed into the lake-drainage. There is no doubt that flava has often been con- 

 founded with trigona (or even undata), and that it actually intergradcs through 

 trigona into undata. 



FUSCONAIA FLAVA TRIGONA (Lea) (1831). 



Quadrula trigona (Lea) Simpson, 1900, p. 787; Quadrula undata (Barnes) (Ohio- 

 form) Walker, 19106, p. 22; Quadrula undata (Barnes) Simpson, 1914, 



p. 880 (pro parte). 



Plate II, fig. 1. 



Records from Pennsylvania: 



Stupakofi, 1894, p. 135 (Allegheny Co.). 



Rhoads, 1899, p. 137 (Ohio River, Coraopolis, Allegheny Co.)-'^ 



Characters of variety: This is a Fusconaia flava which has a more swollen shell, 

 chiefly anteriorly, with a diameter of fifty-five percent of the length or more. In 

 consequence of this the sides of the shell are generally more concave, forming a 

 gentle radial depression in front of the posterior ridge. In other respects there are 

 hardly any differences from the normal form. 



L. H. D. Pr.ct. 



Size: 1. Neville Island, Cat. Xo. 61.18376 67 mm. 52 mm. 38 mm. .57 



2. do. Cat. No. 61.16336 50 " 41 " 31.5 " .63 



According to Lea's figure 59 " 49 " 38 " .64 



The soft parts have never been observed in Pennsylvania. But specimens 

 referable to this form have been found with the soft parts in Elk River, West 

 Virginia, and gravid females were found there on July 8, 1911, with glochidia. 

 The anatomy is absolutely identical with that of F. flava, as are also the gloehidia: 

 L. 0.15 mm., H. 0.16 mm. A form indistinguishable from this was collected by 

 H. E. Wheeler in Saline River, Arkansas (July 13, 1911), and the anatomy and 

 glochidia of this form were the same. 



According to the above dates, the end of the breeding season of this form falls 

 in July. 



Remarks: In this case also I have been compelled to draw an artificial dividing 

 line, at the diameter of fifty-five percent, between two forms, while in nature a 

 gradual transition exists. This is justified by the same practical considerations as 

 in the case of Fusconaia subrotunda and kirtlandiana. Walker specifically unites 

 the present form with undata and he is undoubtedly right. Yet I think we should 

 recognize trigona as a distinct variety, with less developed beaks; while F. flava 

 undata has much elevated and often incurved beaks. The range of the two forms 



■ 1^ I have (19096, p. 183 and 187) questioned the correptness of this record, since Rhoads' specimens 

 are too young. But it should stand, 



