148 THE NAIADES OF MISSOURI 



(Raf.). but, as stated before, it takes the place of the latter wholly 

 in North Missouri. The North Missouri Grand River bears dona- 

 cijormis in its most typical form. The writer finds this species 

 most colonial in their habits, and has been able to find many of 

 them nearly every month of the year, but has not found any 

 gravid during the winter. The earliest date for the bearing of 

 glochidia is June 19th. No previous public record has ever been 

 made of this unique glochidium. From the above data it may be 

 inferred that it is not bradytictic as is mostly the breeding habit 

 of the Lampsilinae. This little mussel is also eccentric in that while 

 in the parasitic stage it develops an adult shell live times the size 

 of the glochidial one. Surber (1913, p. 109) finds that its specific 

 distributor is "Sheep's Head" (^4. grunniens). 



Amygdalonaias truncata (Rafinesque). 



("Deer-Foot," or "Deer-Toe.") 



XXV, Fig. 88 A and B. 



1820 — Unio truncata Rafinesque, Ann. Gen. Sci. Phys. Brux. 



1831 — Unio elegans Lea, Am. Phil. Soc, IV, p. 83., pi. fig. 13. 



1898 — Plagiola elegans Baker, Moll. Chicago, Pr. I, p. 91, pi. XXI, 

 fig. i; 1900b, Simpson, Pr. U. S. Nat. Mus., XXII, p. 604. 



1912b — Amygdalonaias elegans (Lea) Ortmann, An. Car. Mus., XXII, 

 p. 328. 



ANIMAL CHARACTERS. 



Nutritive Structures: — Identical with those of donaciformis. 



Reproductive Structures: — Branchial mantle margin a 

 little more thickened with slight crenulations than in donacijormis; 

 glochidia a little larger, measuring 0.060 x 0.070 mm — otherwise 

 these structures are identical with those of donacijormis. 



SHELL structures. 



External vStructures: — Shell short, roundly triangular, 

 inflated; post-umbonal ridge sharply angulated from beaks to 

 posterior point of shell; disk smooth; beaks rather prominent, 

 sciUptured with a few fine ridges more or less double-looped or 

 sinuated; epidermis yellowish, brownish or even grreenish with 

 beautiful paintings of green broken by arrow-marked rays; no 

 sex dimorphism of shell, both sexes being rather swollen post- 

 ventrad. 



Internal Structures: — With the exception of a deeper and 



