EXPLANATION OF PLATE LXXXVI. 
Horizontal cross-sections through the gills of Unionide, to show structure of water- 
tubes, ovisacs, and septa, in the males, sterile and gravid females. 
All photographs taken with Bausch & Lomb 1 inch objective. None of the figures 
has been retouched. 
Fig. 
Fig. 
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Fig. 
Fig. 
Fig. 
Fig. 
1. Quadrula subrotunda (Lea) Male.—Allegheny River, Kelly, Armstrong County, 
June 22, 1909. Cat. No. 61.4400. Specimen 199. 
la. Left inner gill. 1b. Left outer gill. 
2. Quadrula subrotunda (Lea) Female, sterile—Allegheny River, Kelly, Armstrong 
County, Sept. 5, 1907. Cat. No. 61.3083. Specimen 5. 
la. Left inner gill. 2a. Left outer gill. 
g. 3. Quadrula subrotunda (Lea) Female, gravid (eggs).—Allegheny River, Kelly, 
Armstrong County, June 22, 1909. Cat. No. 61.4899. Specimen 7. 
3a. Right inner gill. 3b. Right outer gill. 
4. Quadrula tuberculata (Barnes). Female, sterile. Mahoning River, Mahoningtown, 
Lawrence County, Aug. 4, 1908. Cat. No. 61.3574. Specimen 34. 
4a. Right inner gill. 4b. Right outer gill. 
5. Elliptio gibbosus (Barnes) Male.—Little Beaver Creek, Enon Valley, Lawrence 
County, May 11, 1907. Cat. No. 61.2186. Specimen 54. 
5a. Left inner gill. 5b. Left outer gill. 
6. Elliptio gibbosus Barnes. Female, gravid (eggs). Allegheny River, Templeton, 
Armstrong County, Aug. 13, 1907. Cat. No. 61.2963. Specimen 56. 
6a. Left inner gill. 6b. Left outer gill. 
7. Strophitus edentulus (Say) Female, sterile. Allegheny River, Templeton, Arm- 
strong County, Aug. 4, 1909. Cat. No. 61.4150. Specimen 117. 
7a. Left inner gill. 7b. Left outer gill. 
8. Strophitus edentulus (Say) Female, gravid, young (eggs), beginning of period of 
gravidity. Conococheague Creek, Greencastle, Franklin, County, Sept. 6, 1909. 
Cat. No. 61.4160. Specimen 112. 
Left outer gill. 
9. Strophitus edentulus (Say) Female, gravid (eggs), a little more advanced than fig. 8. 
Cush-Cushion Creek, Green Township, Indiana County, July 11, 1908. Cat. No. 
61.3627. Specimen 109. j 
Left outer gill. 
10. Strophitus edentulus (Say) Female, sterile, very young (shell 17 mm. long). 
Crooked Creek, Rosston, Armstrong County, Aug. 3, 1909. Cat. No. 61.4148. 
Specimen 230. 
10a. Left inner gill. 10b. Left outer gill. 
340 
