THE NAUTILUS. 19 



pointed out by Dr. Ortmann, even a macrospic examination 

 •will enable one to note that the septa (vertical partitions for the 

 ovisacs) of the sterile marsupium are distinctly more crowded 

 than those that separate the gill chambers of the male gills. 

 A histologic study shows five or ten gill filaments between the 

 septa of the sterile marsupium or brood pouch. 



Tables 2 and 3 are summarized accounts made out from com- 

 plete individual records kept on the regular form issued by the 

 U. S. Bureau of Fisheries for Biological Stations. These indi- 

 vidual accounts of the different species comprehended the sterile 

 females as well as those gravid with early-late embryos and 

 mature-immature glochidia. As proof of this record the author 

 still holds in his possession the preserved anatomical material, 

 gravid with glochidia and also much that is gravid with early 

 and late embryos. The soft parts have been preserved wdth the 

 shells, the latter having been cleaned in a solution of sodium 

 carbonate (NajCOj) made by dissolving five pounds of this 

 chemical in five gallons of water. Then the soft parts were 

 preserved in the marked shells after the right valves were cut 

 loose and temporarily examined afield when the best studies 

 can be made before the tissues are contracted or discolored 

 by the preservative. The best preservative for the whole speci- 

 mens has been found by the author to be 70 or 80 per cent, 

 alcohol, since such preserving fluids as formaldehyde contain 

 so much free acid that the shell is deteriorated by the chemical 

 reaction upon the limy composition. 



While the writer was engaged for over three years in procur- 

 ing data for his illustrated and descriptive catalogue of the 

 Naiades of Missouri ' it was his good fortune to discover a few 

 glochidia, which follow in the descriptive table here, as the 

 first on actual record. The author is indebted to Dr. T. Surber 

 for his acknowledgement of the novelty and also for his verifi- 

 cation of measurements of these glochidia. 



The author is confident that fertilization of the ova takes 

 place in the euprabranchial canals and when more data is at 

 hand this determination may be set forth as a well-proven phe- 



'American Midland Naturalist, Vol. iv, 19]rj-li»l(), Plates 1-XXVIII. 



