42 NAIADES OF MISSOURI 



edge; conglutinates, sole-shaped, brown, rather solid; glochidia 

 large, ventral margin obliquely rounded, hinge line long. 



SHELL CHARACTERS. 



Shell large, ponderous, broadly rhomboid, moderately inflated, 

 post-dorsal ridge alated, sculptured with regular upcurved undu- 

 lations; post-umbonal ridge broken with coarse plications running 

 more or less parallel with it; beaks rather low, sculptured with 

 coarse double looped-corrugations which extend out as nodules at 

 base of post-ridge and as zigzag ridges all over umbonal region to 

 upper part of disk; epidermis black; cardinals heavy; laterals 

 long and straight; interdentum short; beak cavities narrowly 

 deep; scars very deeply impressed — especially anterior retractor 

 cicatrix; nacre white to pink. 



Miscellaneous Remarks: — Because of the peculiarities of 

 heros (Say) as to its animal and shell characters, as well as to its 

 uniqueness of breeding season it is thought by the author in con- 

 ference with other students, that this species of Say, very well deserves 

 rank as the type of a new genus. Although the author has not 

 examined the animal of boykiniana Lea, triuynphans Wright, etc., 

 yet, from shell characters, these allied forms would naturally 

 fall under this new genus, Mcgalonaias. In all probability crassi- 

 dens (Lamarck) [ = trapezoides (Lea)], which has been grouped 

 ver}^ near heros (Say), may also deserve a special compartment, 

 according to the recent opinion of Mr. Frierson, who has made 

 special study of this species abundant beds of which are very 

 accessible to him; hence because of the difference of shell characters 

 of crassidens from that of heros (or from any other Naiad shell 

 in the possession of a " ventral scar" as pointed out by Mr. Frierson) 

 this species of Lamarck is not grouped there. Besides crassidens 

 is not found in Missouri, neither is boykiniana, triumphans and 

 other conchologically allied forms of M. heros and thus the new 

 genus will safely stand out for this State with its type, {heros Say), 

 as the lone representative. Bariosta (Raf.) might be the available 

 name for our new genus, if crassidens could be found to be congen- 

 eric with heros, since Rafinesque erected his genus for this species 

 which he termed ponderosus, but which Mr. Walker, through his 

 close study of Lamarckan types, says is Lamarck's crassidens 

 that ante-dates Lea's trapezoides as well as Rafinesque's type. 

 From the fact that Crenodonta (Schliiter) falls into the synonomy 



