EXPLANATION OF PLATE LXXXVII. 
Horizontal (figs. 1-10) and vertical (figs 11-16) cross-sections through gills of Najades, 
to show structure of water-tubes, ovisacs, and septa, in the males, sterile and gravid females, 
and to show structure of the edge of the gills. 
All photographs taken with Bausch & Lomb 1 inch objective. None has been re- 
touched. 
Fig. 1. Ptychobranchus phaseolus (Hildreth) Male. Loyalhanna River, Idlepark, West- 
moreland County, Sept. 21, 1907. Cat. No. 61.3035. Specimen 119. 
la. Left inner gill. 1b. Left outer gill. 
Fig. 2. Ptychobranchus phaseolus (Hildreth) Female, sterile. Raccoon Creek, New Shef- 
field, Beaver County, June 30, 1908. Cat. No. 61.3275. Specimen 123. 
Left outer gill. 
Fig. 3. Ptychobranchus phaseolus (Hildreth) Female, gravid (eggs). Loyalhanna River, 
Idlepark, Westmoreland County, Sept. 21, 1907. Cat. No. 61.3035. Specimen 120. 
Left outer gill. 
Fig. 4. Plagiola securis (Lea) Male. Allegheny River, Kelly, Armstrong County, Sept. 
5, 1907. Cat. No. 61.3029. Specimen 127. 
4a. Left inner gill. 46. Left outer gill. 
Fig. 5. Plagiola securis (Lea) Female, gravid (glochidia). Ohio River, Cooks Ferry, 
Beaver County, Sept. 10, 1908. Cat. No. 61.3565. Specimen 129. 
Left outer gill. 
Fig. 6. Paraptera gracilis (Barnes) Female, sterile. Ohio River, Industry, Beaver County, 
Sept. 8, 1908. Cat. No. 61.3549. Specimen 137. 
Left outer gill. 
Fig. 7. Lampsilis iris (Lea) Female, sterile. Presque Isle Bay, Lake Erie, Erie, Erie 
County, May 22, 1909. Cat. No. 61.4090. Specimen 144. 
Left outer gill. 
Fig. 8. Lampsilis recta (Lamarck) Male. Cheat River, Cheat Haven, Fayette County, 
Sept. 16, 1907. Cat. No. 61.3020. Specimen 149. 
8a. Left inner gill. 8b. Left outer gill. 
Fig. 9. Lampsilis recta (Lamarck) Female, sterile. Cheat River, Cheat Haven, Fayette 
County, July 10, 1908. Cat. No. 61.8509. Specimen 246. 
Left outer gill. 
Fig. 10. Lampsilis ventricosa (Barnes) Female, sterile. Little Beaver Creek, Enon Valley, 
Lawrence County, May 11, 1907. Cat. No. 61.2144. Specimen 168. 
Left outer gill. 
Fig. 11. Margaritana margaritifera (Linneus). Indian Run, Rene Mont, Schuylkill 
County, May 4, 1909. Cat. No. 61.4272. Specimen 200. 
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