THE NAUTILUS. 53 



mens, although there is a much greater range of variation in the 

 latter. The Potomac specimens are rather high and short, and their 

 size remains far below that of western ventricosa. My largest speci- 

 men (a male from Hancock) is 114 mm. long, 82 mm. high, and 58 

 mm. in diameter, while I have many individuals from western Penn- 

 sylvania, which are 150 mm. long and over. Further the posterior 

 ridge of the shell is in the Potomac form a little more distinct than 

 in the average of the western specimens, but again in this character 

 there are western specimens, which agree with the eastern. 



In all other particulars the two forms agree, and also the color 

 and color markings (rays) of the epidermis are the same, and quite 

 variable. But on account of the small size, the shorter and higher 

 outline, and somewhat more distinct posterior ridge, we might regard 

 the Potomac-race as a variety, which I propose to call : Lampsilis 

 ventricosa cohongoronta (an old Indian name of the Potomac). I 

 may add, that I have investigated the anatomy, of males, sterile and 

 gravid females, and that there is no difference whatever. Also the 

 glochidia are the same. 



It is evident that this shell is, zoogeographically, out of place in 

 the Potomac, and, considered together with the case of the western 

 crawfish mentioned above, we must conclude that both are artificial 

 introductions into this river, probably quite accidental, and the idea 

 is suggested that the shell might have been transported in the larval 

 stage, as glochidium, during its parasitic life upon certain fishes. 

 Western species of fishes have repeatedly been transplanted into the 

 Potomac system. H. M. Smith and B. A. Bean (Bull. U. S. Fish 

 Comm. 18 (or 1898) 1899 pp. 179-187) mention no less than seven 

 species (disregarding four European), and among them are the fol- 

 lowing : Rock Bass (Ambloplites rupestris (Raf.)), Large mouth 

 Black Bass Micropterus salmoides (Lac.), and Crappie (Pomoxis 

 annularis Raf.). 



Now just these have recently been given by G. Lefevre and W. C. 

 Curtis (Bull. Bur. Fisheries, 30, 1912, pp. 157 and 160) as most 

 susceptible to infection with the glochidia of species ot Lampsilis, 

 among them Lampsilis ventricosa. The introduction of Black Bass 

 was in the Shenandoah River in 1889; that of the other two fishes 

 in various parts of the Potomac and the Chesapeake-Ohio Canal 

 chiefly in 1894. I do not hesitate to attribute to this fact, the trans- 

 plantation of certain western fishes, the accidental introduction of 



