126 THE AMERICAN MIDLAND NATURALIST 
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 0.340mm.* 
Fic. 3A. Mature glochidium of M. heros showing peculiar oblique 
post-ventral margin from lateral view. (x87—a camera 
lucida sketch. Left hand figure.) 
Fic. 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 
dium has the greatest variation in size and moreover, he has also found 
it parasitic upon the gills of the ‘‘water dog’’ (Necturus maculosus). 
