358 



Annals of the Carnegie Museum. 



Truncilla rangiana (Lea). 



Six males, four sterile and four gravid females, from the upper 

 Allegheny River drainage in Pennsylvania, are at hand. 



The gravid females, with eggs and glochidia, were found in 

 September. 



This form is generally regarded as a variety of T. per plexa, but Walker 

 (1910c) separates it as a species. All specimens examined by me are 

 true rangiana, but they do not agree with the characters given in 

 Walker's key (/. c, p. 80), since the color and texture of the marsupial 

 expansion is, in old females, quite different from the rest of the shell, 

 being horny and lacking in lime. In young females, this is not the 

 case. 



As to the soft parts, see Ortmann (191 16, p. 322), and also those of 

 perplexa, described by Lea (Obs., X, 1863, p. 420). 



Fig. 28. Truncilla rangiana (Lea). Gravid female, from French Creek, Cochran- 

 ton, Crawford Co., Pa. (Cam. Mus., No. 61, 3,363.) Coll. Sept. 2, 1908. 



Anal, supra-anal, palpi, structure of gills, and marsupium generally 

 as in T. triquetra. The marsupium is greatly swollen, rather low and 

 long, not so much deformed. Glochidia (figured as of perplexa by Lea, 

 Obs., VI, 1858, pi. 5, fig. 21) are also similar; length 0.26; height 

 0.23 mm., but my measurements are not very accurate, since all the 

 glochidia I have are very young and delicate. 



In the female, the two edges of the mantle diverge greatly in front 

 of the branchial, the outer one curving outward, and forming a great, 

 almost semicircular lobe, with a smooth edge; while the inner one runs 

 almost straight downward and forward; the two edges coming together 



