44 



NAIADES OF MISSOURI 



connection; anus tentacled: gills very long and large, inner much 

 wider, inner lamina free from visceral mass for the posterior half 

 or connected except for a slight slit at posterior end or even entirely 

 connected; palpi enormous, connected about nine-tenths of their 

 length antero-dorsad; soft parts mostly a fleshly-tan, branchial 

 edges brown with yellowish papillae in incurrent opening, patch 

 in front of branchial opening chamois-like. 



Reproductive Structures:- — Marsupia occupying all four 

 gills; when gravid, enormous purplish pads, obtusely rounded at 

 ventral edges; ovisacs simple, undivided, some filled with rusty- 

 brown mucus next to the laminae thus giving the marsupia a 

 splotched appearance; conglutinates shape of an insole, rather 

 solid, usually discharged whole, edges with brownish red pigment, 

 rather thick with no thin transparent portions; glochidia large, 

 post-ventral border obliquely rounded, hinge line long, nearly 

 straight, no spines present, very vital, measures 0.280 x o.34omra,' 



Fig. 3A. Mature glochidium of M. heros showing peculiar oblique 

 post-ventral margin from lateral view. (xSy — a camera 

 lucida sketch. Left hand figure.) 



Fig. 3B Ventral view of open glochidium of M. heros. (X87 — a 

 camera lucida sketch. Right hand figure.) 



SHELL CHARACTERS. 



External Structures: — Shell massive, heavy, subrhom- 

 boid, post-dorsal ridge rather high slopes of which ribbed with 

 coarse, upcurved, regular undulations originating from umbonal 

 region; post umbonal ridge broken with heavy undulations more 



^ According to Dr. T. Surber, (U.S. B.F. Doc, No. 813, 191 5) this glochi- 

 dium has the greatest variation in size and moreover, he has also found 

 it parasitic upon the gills of the "water dog" (Nec/wrMS ntaculosus). 



