NAIADES OF MISSOURI Ti3 
(1913, p. 104) finds the host that is the specific distributor of this 
valuable shell to be a fish known as ‘“‘skipjack’’ (Pomolobus 
chrysochloris). . 
Genus Amblema Rafinesque. 
1820—Amblema Rafinesque, Monograph Biv. Shells of R. Ohio. 
1912b—Crenodonta (Schluter) Ortmann, An. Car. Mus., VIII, pp. 
245-250. 
(Type Unio plicata |Lesneur] Say). 
ANIMAL CHARACTERS:—Branchial opening long with few 
small arboreal papillae; anal large, very slightly crenulated; 
supra-anal separated from anal by very short mantle connection, 
sometimes no connection at all; gills large, inner wider and longer, 
outer connected high up to mantle antero-ventrad, inner laminae 
of inner gills free from visceral mass; palpi long, falcate united 
most of their length antero-dorsad; marsupia occupy all four 
gills, ovisacs of inner being wider, when gravid ovisacs expand 
transversely; conglutinates white, compressed, leaf-like shape, 
discharged through anal passage in rather broken or loose masses; 
glochidia small, spineless, subovate. 
SHELL CHARACTERS:—Shell subquadrate to subtrapezoidal, 
thick, beaks more or less elevated, sculptured with concentric 
‘lines slightly angled at the base of the post-umbonal ridge and 
disappearing out upon the disk or continued there in a zigzag 
pattern of irregular broken pustules, nodules and oblique, indu- 
lated or plicated folds, the latter being disposed across the pos- 
terior half; hinge teeth heavy and well developed; beak cavities 
deep crevices under rather wide interdentum; vein markings 
on antero-pallial margin distinct; nacre usually white. 
MISCELLANEOUS REMARKS:—It is recognized by students 
of Nazades that this genus needs a thorough revision—especially 
as to its shell characters. Like the genus Pusconaia, Amblema is 
a group of all sorts of inter-grading and puzzling forms. However, 
for this State it is not so much a question of facts regarding a 
predominance of these plicated forms for the different faunae as 
it is an application of these varieties to the present chaotic no- 
menclature for this genus. As nearly as the writer is able to 
determine, after a correspondence with students and a thorough 
study of literature and actual field conditions, the present status 
of affairs would group the species and other allied forms of Amblema 
