V 



no THE NAIADES OF MISSOURI 



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.) 



c? 63 X 34 X 31 " X 0.340 (Lower Lake, St. Joseph, Mo.) 



9 61 X 28 X 35 " X 0.360 (Spring Lake, Monegaw Spgs. Mo.) 



cf 25 X 10 X 2 " X 0.330 (Mud 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 Naiades. 

 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 Jiermaphoroditic gives it a character possessed 

 by few Naiades. 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 distinctlv 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)- 



