140 MEMOIRS OF THE CARNEGIE MUSEUM. 



Lea, lewisi Lea, salmonia Lea, harpethensis Lea simply are synonyms) is a shell 

 preferably inhabiting small creeks. It is chiefly characterized by its rather elon- 

 gated, subovate shape, with rather flat valves, by the comparative solidity of the 

 shell, its dark (greenish to blackish) color, and the nodulous character of the beak- 

 sculpture. The posterior end of the shell generally is narrowed, and the posterior 

 point is moderately elevated above the base line ; and there is hardly a wing (how- 

 ever, this is sometimes indicated in the young). Yet all these characters are 

 variable, and certain extreme forms are found under peculiar conditions of environ- 

 ment, so that they are to be regarded as ecological variations, which turn up, 

 within the range of the species, wherever the proper conditions are found. A 

 number of them have received names; but these names should not be used as 

 varietal names, since the forms designated by them have no defined geographical 

 areas. They certainly are not "subspecies" in the strict taxonomic sense. I shall 

 mention here some of these "forms," as far as they are found in Pennsylvania, 

 with the express understanding, that I regard them only as individual variations, 

 or at the utmost as special reactions to peculiar environmental conditions, which 

 are not regionally restricted. 



Anodonta grandis forma salmonia (Lea) (Obs. II, 1838, PL 14, fig. 41). 



This is an unqualifiedly typical grandis, with the nacre peculiarly discolored 

 (reddish, from pale salmon to deep rusty red), and at the same time the nacre 

 becomes rough by the formation of small pustules and granulations. That this 

 is due to an infection by a parasite (a distomid) is now generally conceded (see 

 Wilson & Clark, 1912a, p. 47), and consequently the name salmonia has no tax- 

 onomic standing, and might better be entirely dropped. 



In Pennsylvania, such diseased forms are rather frequent in the northwestern 

 corner of the state (headwaters of Beaver system, and small tributaries of the 

 upper Allegheny), but are absent in the southwestern section. Sometimes traces 

 of this disease are found in pond- and lake-forms. At certain localities, practically 

 all individuals are more or less infected with this parasite. 



Anodonta grandis forma gigantea (Lea) (1834) (Simpson, 1914, p. 420). 



This is the form found in small, muddy pools, where it lives deeply buried in 

 black muck. It is distinguished from the creek-form by its larger size, thinner, 

 and higher and less elongated shell, and generally by more vivid color (yellowish 

 and greenish concentric bands, and more distinct traces of rays). However, this 

 form also is very variable, even in the same pond, and it passes insensibly into the 

 creek-form. In ponds more elongated specimens are often found, and in creeks 

 specimens from quiet and muddy pools distinctly incline toward the pond-form. 

 Specimens from ponds often also possess a rather thick shell. 



