io8 The naiades of Missouri 



as to whether any of the lacustrine Anodontinae are byssiferous, 

 since the quiet water of the lake would perhaps make these threads 

 unnecessary. The specimen above measured has a very thin,, 

 papery shell, almost transparent; ground-glass-like inside view, 

 yellow-horn color outside appearance, beautifully rayed in green 

 especially on post-umbonal slope. In life the heart beat could be 

 detected through the thin shell and the alimentary tract traced; 

 the heart beat 28 times per minute, regular but feeble, while that 

 of an adult was only twenty-two times per minute, irregular but 

 strong. 



Miscellaneous Remarks: — This species is especially charac- 

 teristic for the shape of its shell being not variable, but somewhat 

 like an ordinary dinner plate as to form and size; also the very 

 distinct progressive impressions are somewhat characteristic. 

 Its shell is the largest in outline of any of the Naiades, although it 

 is not heavy, — even with its soft parts. Its meat has been tested 

 through Domestic Science to be of great food value. Except for 

 greater inflation, in case of the female shell, no real sex dimorphism 

 can be detected. The author has noted more of a greenish granular 

 appearance for the outer gills of the male. The fact that the writer 

 has discovered, from aquarium observations, individuals discharg- 

 ing sperm on two occasions disproves that it is hermaphroditic . For 

 reference one of these males was killed and preserved in the act 

 of discharging its sperm. 



This discharge of sperm made the water milky and when 

 examined by a high-power (X385) lens it was observed to be the 

 flagellated sperm in cysts rolling about through the water like the 

 colonial Protozoa. Then, too, the simple test that not all indivi- 

 duals have the crowded septa of the outer gills disproves that all have 

 marsupial characters of these gills. Thus hermaphroditism can not 

 he applied to this genus Lastena, as a general character, li this species 

 is to remain with it. This is the first description of the animal of 

 this species that has been drawn up and the author has been the first 

 to report its mature glochidium which in general shape is about like 

 that of A. grandis having about the same shape with the same 

 straight hinge line, but being smaller. The glochidium is very 

 active, having been observed to snap fifteen times per minute. 

 The habitat of suborbiculata is that of black sand and mud bottoms 

 in deep quiet water, is a rare shell in general distribution, but, 

 when found, is abundant. Simpson reports it for Nebraska, Iowa, 



