356 MEMOIRS OF THE CARNEGIE MUSEUM. 



EXPLANATION OF PLATE VII. 



All figures are three-fourths natural size, a, lateral view; h, dorsal view. 



Fig. I. Pleurobema obliquum cordatum (Rafinesque). This specimen most closely 

 approaches this form, but is not quite typical. From the Allegheny River, Godfrey, 

 Armstrong Co., Pennsylvania, collected August 10, 1909; C. M. Cat. No. 61.4378. 



Fig. 2. Pleurobema obliquum catiUus (Conrad). Female, diameter 52 percent of 

 length, approaching the var. coccineum (Conrad). From the Allegheny River, Godfrey, 

 Armstrong Co., Pennsylvania, collected July 27, 1910; C. M. Cat. No. 61.4567. 



Fig. 3. Pleurobema obliquum coccineum (Conrad). Large specimen, diameter 42 

 percent of length, from French Creek, Cambridge Springs, Crawford Co., Pennsylvania, 

 collected September 13, 1909; C. M. Cat. No. 61.4394. 



Fig. 4. Pleurobema obliquum coccineum (Conrad). Younger specimen, diameter 

 45 percent of length, from French Creek, Cambridge Springs, Crawford Co., Pennsyl- 

 vania, collected September 13, 1909; C. M. Cat. No. 61.4394. 



Fig. 5. Pleurobema obliquum coccineum (Conrad). Topotype, diameter 46 per- 

 cent of length, from Mahoning River, Mahoningtown, Lawrence Co., Pennsylvania, 

 collected August 4, 1908; C. M. Cat. No. 61.3907. 



Fig. 6. Pleurobema obliquum pauperculum (Simpson). Typical, large specimen, 

 diameter 47 percent of length, from Lake Erie, Presque Isle Bay, Erie, Erie Co., Penn- 

 sylvania, collected May 21, 1909; C. M. Cat. No. 61.4398. 



Fig. 7. Pleurobema clava (Lamarck). Large, gravid female from Neshannock 

 Creek, Eastbrook, Lawrence Co., Pennsylvania, collected June 18, 1908; C. M. Cat. No. 

 61.3335. 



Fig. 8. Pleurobema clava (Lamarck). Smaller specimen, very oblique, from 

 Shenango River, Clarksville, Mercer Co., Pennsylvania, collected September 21, 1908; 

 C. M. Cat. No. 61.3814. 



Fig. 9. Pleurobema clava (Lamarck). Small specimen, much less oblique, from 

 Shenango River, Clarksville, Mercer Co., Pennsylvania, collected September 21, 1908; 

 C. M. Cat. No. 61.3814. 



Note: The rays and blotches present in the specimens in figs. 7, 8, and 9, did not 

 come out in the photographs. 



