15^ THE NAIADES OF MISSOURI 



very solid; glochidia very small, sub-ovate; spineless, hinge 

 line short, slightly curved. 



Shell Characters: — Shell thin, sub-elliptical, alated, com- 

 pressed; post-umbonal ridge lacking; disk smooth; unbones 

 low marked with fine concentric lines followed by later double- 

 looped bars; epidermis glistening tawny, rayed; sex-dimorphism 

 shown in wider more blunt vertically at posterior end of female 

 shell; hinge teeth reduced to rudiments. 



Miscellaneous Remarks: — This genus is also constructed 

 on the basis of characters relating to shell and glochidia rather 

 than to anatomical structures. On basis of glochidial characters 

 alone it classes with Amygdalonaias; however its shell characters 

 throw it near to the genus Proptera. Lasmonos is represented 

 in this vState by its type (which is the commonest shell in North 

 Missouri) and by simpsoni Feriss. The latter is grouped here 

 tentatively until its soft parts are studied as its shell characters 

 more closely relate it to the type of this genus than to any other. 

 The species, Leptodea leptodon Rafinesque, is perhaps congeneric 

 here and much depends upon its marsupial and glochidial characters, 

 which are as yet unknown; however, the writer has not been 

 fortunate enough to secure live specimens of this species (not 

 even dead shells) in this State, but, because of the use Rafinesque 

 made of it, we are concerned here for nomenclatural reasons, 

 Jor should it be found to he really congeneric with Jragilis, aside from 

 its several shell characters, the generic name, Leptodea, would take 

 preference to the one herein used. 



Lasmonos fragilis Rafinesque. 



("Paper Shell," "Razor Back.") 



PL IX, Fig. 19; PI. XXVI, Figs. 90 A—D. 



1820 — Lasmonos fragilis Rafinesque, Mono. Biv. of Ohio. 



1823 — Unio gracilis Barnes, Am. JL Sci., VI, p. 274. 



1861 — Unio dolosus Lea, JL PhiL Ac, V, p. 75. 



1900b — Lampsilis gracilis Simpson, Pr. U. S. Nat. Mus., XXII, p. 573 



1912b — Paraptera gracilis Ortmann, An. Car. Mus., VIII, p. 331. 



ANIMAL CHARACTERS. 



Nutritive Structures: — Branchial opening round, with 

 spreading, yellowish tentacles ; anal slightly crenulated, with thick- 

 ened edges and normal diaphragm; supra-anal long, extending to 

 dorsal ala, usually closed; mantles parallel at edges, dark colored 



