THE NAIADES OF MISSOURI 261 
scars faintly impressed, confluent; branchial cavities large; nacre 
pearl blue. 
Sex Length Height Diameter Um.ra. Locality 
9 98 x 40- x 39mm x 0.320 (Mud Lake, Kenmoor, Mo.) 
oaeeos ) S34 = (ar ” “x 0.440 . (Lower Lake, St. Joseph, Mo.) 
9 61 x 28 x 35 ” x 0.360 (Spring Lake, Monegaw Spgs. Mo.) 
maa Kk) 1rO ix, 2'’ «&.0.3¢0 \(Mad Lake, Halls, Mo.) 
The latter juveniles of the last measurement has the least 
diameter that the author has ever examined. It was discovered in 
very active locomotion in shallow water along the lake beach and 
wonder was expressed how such a compressed shell could contain 
enough musculature for such vitality. Its beak sculpture presents 
two apiculations at the apex of the umbone surrounded by rather 
wavy or looped bars extending low to the disk. So thin were the 
valves and soft parts that when studied with the lens the heart 
action could be observed through the shell when held up to the 
light. The characteristic green rays, extending parallel along the 
post umbonal ridge area, are more pronounced here than in the 
adult shell. 
MISCELLANEOUS REMARKS:—The vitality of ohiensis of the 
embryos in the active rotary motion is seldom seen in the Nazades. 
This motion was observed to take place around one axis from 
right to left in very rapid rotation. Mr. L. S. Frierson states that 
he has seen the glochidium taken from the mother and so suffici- 
ently metamorphosed as to turn its shell up from a glass slide 
through an angle of 180 degrees.* The fact, too, of this species 
being normally hermaphoroditic gives it a character possessed 
by few Nazades. ‘The adult shell is also so peculiar that there is 
no need for confusion in making identification. The nearest to 
it in general form and color is Lasmonos leptodon, yet it can be 
easily distinguished from this distant relative by the beak sculp- 
ture and hinge. Its suppressed umbones flush with the dorsal 
line, making ‘“‘beakless beaks,’’ are perhaps its recognition marks. 
It is a lover of quiet, shallow water and muddy bottoms and for 
this reason is distinctly lacustrine. The author has found it in 
* Dr. A. D. Howard has lately discovered Lastena ohiensis as also non- 
parasitic in its glochidial life and accounts for its distribution through the 
buoyancy of its juvenile shell as a compsensatory provision for the loss of 
the usual means of distribution by fishes. (Science, N. S., XL, pp. 353- 
355, Sept. 4, 1914). 
