ORTMANN: monograph of the naiades of PENNSYLVANIA. 2/ 



Soft parts (See Ortmann, 1912, p. 246). Glochidia unknown. 



Breeding season: Of this form, I have found only two gravid females, with 

 eggs, on July 8, 1910. The eggs were white. 



Remarks: The nomenclature of this species and its forms has been erroneous 

 hitherto, and the original U. plicalus of Say has been entirely misunderstood by 

 practically all authors, except Utterback (1916). Indeed, from Say's description 

 alone it is impossible to decide what form of the pZicato-group he had before hun, 

 but the locality he gives. Lake Erie, settles the case. There is no other form of 

 the pUcata-group in the lake,^^ except this, and consequently the common form 

 from Lake Erie should bear this name, and not that of hippopa^a given by Lea. 



A. pUcata of Lake Erie is not the normal type of the species, but is a dwarfed 

 form of a species of the Ohio-drainage {costata). Thus nomenclature reverses the 

 natural conditions, making out of a local race the typical form of the species, but 

 this cannot be helped. The differences of A. plicata from the Ohio-form costata 

 are very slight, in fact, the only reliable distinction is the size, but there are a few 

 others, which may be more or less depended upon. The typical plicata is generally 

 more oval, and the posterior part (wing) is not so elevated. Fiu-thermore the 

 growth-lines are more regular and closer together, the shell is slightly more swollen 

 on the average, and the color Ughter. But in young specimens all these characters 

 are more or less obscured, and it is practically impossible to distinguish these two 

 forms in the juvenile stage. I have young costata which may be matched with 

 young plicata, without showing the slightest difference. 



Localities represented in the Carnegie Museum: 



Lake Erie, Presque Isle Bay, Erie, Erie Co., Pennsylvania. 



Lake Erie, Cedar Point and Sandusky Bay, Erie Co., Ohio (0. E. Jennings and Chas. Brookover). 



Lake Erie, La Plaisance Bay, Monroe Co., Micliigan (C. Goodrich). 



Distribution and Ecologij (See fig. 4). Type locality: Lake Erie (Say). 



This species is known in Pennsylvania only from Lake Erie. In Presque Isle 

 Bay it is rather abundant, and at certain places sometimes great numbers of 3'oimg 

 shells are found in one to two feet of water. The larger specimens are generaUy 

 found at a depth of three to four feet, and with the clam-dredge I obtained some 

 at five feet, and* others were brought up by the " sand-sucker " from a depth 

 of ten to fifteen feet. They are found generally in fine sand and gravel, but I 

 also found a few on the southern shore of the bay (mainland), where the bottom 

 consists of coarse shingle. 



=» I have received, from L. S. Frierson, a true A. plicata costata from Maumee Bay at the mouth of 

 the Ottawa River, near Toledo, Lucas Co., Ohio. This however, is a dead shell, and may have been 

 washed into the lake from the Ottawa or Maumee Rivers, in- both of which .1. plicata costata is present. 



