ORTMANN: monograph of the naiades of PENNSYLVANIA. 85 



strongly procurved, and situated at the anterior end of the shell. Radial furrow- 

 more or less distinct. Diameter generally considerably over fifty percent of the 

 length, but sometimes less. Nacre typically red, but sometimes pinkish or white. 



L. II. I). Pr.ct. 



Size: 1. Industry, Cat. No. 61.3S9G !»I mm. 7.3 mm. 54 mm. ..59 



2. Kelly, Cat. No. 61.3079 86 " 71 " 47 " .5.5 



3. Godfrey, Cat. No. 61.3891 63 " .53 " 36 " .57 



Soft parts (See Ortmann, 1912, p. 264) : Glochidia not yet observed. 



Breeding season: Gravid specimens are at hand collected on May 25, 1914 and 

 July 28, 1913. They all had eggs only. 



Remarks: There is not the slightest doubt that this is in Pennsylvania only 

 an individual variation of P. obliquum, characterized by excessive obliquity. 

 There is great variation in this respect, and complete connection with the main 

 form. While the nacre is mostly red in typical specimens from the Tennessee, 

 in Pennsylvania it is more frequently pink or whitish. Altogether, typical rubrum 

 is quite scarce in our state, but, as our fig. 7 on PI. VI shows, it is present, and does 

 not differ at all from specimens from the Tennessee. The intergrades toward 

 P. obliquum are much more abundant with us. 



Considering the conditions in Pennsylvania alone, I should never have thought 

 of giving this form varietal rank. But in other regions, it is more distinctly marked, 

 as for instance in the Upper Tennessee-drainage. Here the var. rubrum in its 

 typical phase is quite abundant and rather sharply distinguished. How^ever, 

 here also are found forms representing transitions to obliquum and catillus. In 

 the region west of the Mississippi, where P. obliquum is practically missing, the 

 var. rubrum (and catillus) are found in its place, and thus it seems to be advisable 

 to retain rubrum as a distinct variety. These western forms require still closer 

 study. 



I w'ant to emphasize this instance, for it demonstrates that a certain form may 

 be in a certain region an individual variation of another form, while in other regions 

 it becomes a better defined local race, or variety. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Ohio River. ShippiuKport and Industry, Beaver Co.; Neville Island, .\llegheny Co. 

 Allegheny River, Godfrey and Kelly, Armstrong Co. 



Other localities represented in the Carnegie Museum: 



Ohio-drainage: 

 Ohio River, St. Marys, Pleasants Co., West Virginia; Portsmouth, Scioto Co., Ohio. 

 Tuscarawas River, Ohio (Holland collection). 

 West Fork of White River, Riverside, Greene Co., Indiana (J. D. Hascman). 



