46 NAIADES OF MISSOURI 



author sees fit to create a new genus for heros of Say:— 



I. — An unusuatty heavy shell, with zigzag or V-shaped, 



sculpturing on upper part of disk and corrugate scupture 



on beaks. 



2. — A tendency of the inner laminae of the inner gills to 



become more or less united with the visceral mass. 

 3.^The gravid marsupium an enormously distended pad, 

 colored purplish, or slaty, with reddish splotches here and 

 there parallel to the septa. 

 4. — Thick, sole-shaped, subsolid conglutinates with rusty- 

 brown margins discharged more or less whole with glochi- 

 dialying all through the conglutinated mass. 

 5. — A large, vital glochidium with post-ventral margin ob- 

 liquely rounded. 

 6. — Breeding season intermediate, or tachytictic with late 

 season (i. e., bearing glochidia in late winter but being 

 sterile during the summer.) 



From Amblema this peculiar species must be removed on 

 account of its beak sculpture which is more like that of Quadrula — 

 especiallv of the " Lachrymosa" group, yet it is separated from 

 the latter chiefly by its ponderous shell and rugose, V-shaped 

 sculpturing on the umbonal region and upper part of disk. It 

 has been grouped under Amblema more on account of the oblique 

 folds on post-half of its shell; however, these plications are, after 

 all, usually disposed differently with respect to the post-umbonal 

 ridge and are not so constant and numerous, nor do they appear 

 so early in the life history of the shell, as in the type for Amblema. 

 The special reason that a new genus should be built for heros is 

 on the basis of its unique character of soft parts. No other generic 

 type of Unioninae (nor of any of the Naiades for that matter) 

 possesses such peculiarities of form, color or size for its marsupium, 

 conglutinate or glochidium; and as to its nutritive structures, 

 none are so eccentric regarding the connection of the inner laminae 

 to its inner gills. Its idiosyncrasy of breeding habits would not 

 only give it a special station, aside from all other Naiades so far 

 known, vet this physiological character may account for its oddity 

 morphologically. The author has kept an accurate breeding 

 record of heros throughout the year — especially for the 

 winter months when other records have been incomplete — to 

 find it gravid with ova of early embryos in fall and early winter, 



