ORTMANN: monograph of the naiades of PENNSYLVANIA. 159 



Middlebury, Addison Co., Vermont, and INIarshall (1895) from Benson, Rutland 

 Co., Vermont. It is also present in Rhode Island (Carpenter, 1890), and is frequent 

 in the western and central parts of Massachusetts (Gould-Binney, 1870). Thence 

 southward it becomes rather common, but south of Pennsylvania records become 

 scarce. No positive localities are at hand from Maryland. From Delaware it 

 has been mentioned by Rhoads (1904), and the localities from Virginia and North 

 Carolina are few. I have found it in the Potomac-drainage in West Virginia and 

 Virginia. According to Simpson it goes only to North Carolina, but there are 

 old records given by Lea for his virgulata and ivilliamsi from Georgia, so that the 

 southern boundary of this species becomes obscure; in addition a number of 

 closely allied forms or species have been described from the southern states, the 

 standing of which remains to be investigated. 



We must regard A. cataracta as a form characteristic of the northern section 

 of the Atlantic Coastal Plain and the Piedmont Plateau, from which center it has 

 spread more or less toward the Allegheny Mountains, but without crossing the 

 divide; and from which it has widely spread, probably in Postglacial times, to the 

 northeast and north, and also slightly northwestwards, reaching New England 

 and the lower St. Lawrence basin, where it has met the eastward expansion of the 

 western A. grandis (See Ortmann, 1913a). 



Anodonta implicata Say (1829). 

 Anodonta implicata Say, Simpson, 1914, p. 391. 



Plate XI, figs. 2, 3. 

 Records from Pennsylvania: 



Lea, 1838 (Schuylkill River, Philadelphia) (as A. newtonensis). 



Gabb, 1861 (League Island, Philadelphia). 



Hartman & jMichener, 1874 (Schu.vlkill River, Chester Co.). 



Marshall, 1895 (Philadelphia). 



Ortmann, 19096, p. 206. 



Characters of the shell: Large, elongated, similar in shape to the pond-form 

 of A. cataracta, but with the posterior end not so elevated; rather thick-shelled, 

 and noticeably thickened along the lower anterior margin (from the middle for- 

 wards). Nacre more or less reddish, or salmon-color. 



It is also said that the shell is more inflated (subcylindrical) than in A. catar- 

 acta, and that the color of the epidermis is lighter (yellowish) and has no rays. 

 This, however, probably is not always the case. Marshall (1890) says, that the 

 beak-sculpture is also different, with the sinus less developed, being gentle in the 



