EXPLANATION OF PLATE LXXXVIII. 
Vertical (figs. 1-5, 10, 12-18, 20, 21) and longitudinal (figs. 6-9, 11, 19) cross-sections 
through the gills of Unionide, to show structure of ovisacs, septa, and edges of gills in 
males, sterile and gravid females. 
All photographs taken with Bausch & Lomb 1 inch objective. None has been re- 
touched. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
1. Elliptio gibbosus (Barnes) Female, gravid (eggs). Allegheny River, Templeton, 
Armstrong County, Aug. 13, 1907. Cat. No. 61.2963. Specimen 56 (Same as pl. 
LXXXVI, fig. 6). 
Left outer gill. 
2. Alasmidonta undulata (Say) Female, gravid (eggs), beginning of gravidity. West 
Branch Mahantango Creek, Richfield, Juniata County, July 18, 1908. Cat. No. 
61.3713. Specimen 75. 
2a. Right inner gill. 2b. Right outer gill. 
3. Alasmidonta undulata (Say) Female, gravid (glochidia) fully charged. Schuylkill 
Canal, Manayunk, Philadelphia County, April 24, 1909. Cat. No. 61.4240. Speci- 
men 206. 
3a. Base of left outer gill. 3b. Edge of left outer gill. 
4. Strophitus edentulus (Say) Female, sterile. Allegheny River, Templeton, Arm- 
strong County, Aug. 4, 1909. Cat. No. 61.4150. Specimen 117 (Same as Pl. LXXXVI, 
fig. 7). 
Right outer gill. 
5. Strophitus edentulus (Say) Female, gravid (glochidia), fully charged. Newmans 
Branch, Wadsworth, Butler County, April 17, 1908. Cat. No. 61.3276. Specimen 
201. 
Left outer gill. 
6. Strophitus edentulus (Say) Same specimen as fig. 4. 
Left outer gill. 
7. Strophitus edentulus (Say) Female, gravid (eggs), beginning of gravidity. Allegheny 
River, Templeton, Armstrong County, Aug. 4, 1909. Cat. No. 61.4150. Specimen 
116. 
Left outer gill. 
8. Strophitus edentulus (Say) Female, gravid (glochidia), more advanced. Shenango 
River, Linesville, Crawford County, Oct. 10,1907. Cat. No. 61.3118. Specimen 202. 
Left outer gill. 
9. Strophitus edentulus (Say) Same specimen as fig. 5. 
Left outer gill. 
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