THE NAIADES OF MISSOURI 259 
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 Nazades, 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 1s 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 indiv- 
duals have the crowded septa of the outer gills disproves that all have 
marsupial characters of these gills. Thus hermaphroditism can not 
be applied to this genus Lastena, as a general character, if 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 1ts 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, 
