584 NEW SPECIES OF PAL#HOZOIC FOSSILS. 
CHONETES (?) IOWENSIS (N. 8.) 
(Tab. III. a, fig. 7.) 
Specific character.—Shell minute, about a quarter of an inch wide, and three-quarters of an inch 
deep ; surface nearly smooth, with a few faint concentric lines of increase. It is possible that this fossil 
may be a minute species of Strophodonta ; the spines of the hinge-line not being visible, and the shell 
being embedded so as to conceal the ventral valve, and prevent a view of the cardinal area, it is difficult 
to form a correct opinion in regard to it. Occurs on the Iowa River. 
PRODUCTUS NEBRASCENSIS. (N. 8.) 
(Tab. V., fig. 3.) 
Specific character.—In general shape, contour, and sinus, this Productus approaches P. Humboldti ; 
but it is rather smaller, and differs in the structure of the surface, which, in the dorsal valve, is promi- 
nently and interruptedly ribbed, as if by the growth of spines directed downwards, and adhering for some 
distance to the surface, the intervals being the points where they were thrown off; these intervals are 
arranged in three or four concentric rows. | Ventral valve pitted in numerous concentric rows, with inter- 
mediate concentric transverse lamelle. 
From the carboniferous limestone, Bellevue, Missouri River, Nebraska. 
LEPTHNA TRILOBATA. (N. 8.) 
(Tab. IL., figs. 17, 18.) 
Specific character.—This species was at first referred to the species deltoidea, but the form is so 
decidedly different in several respects, that it seems to constitute a distinct species. Dorsal valve broadly 
trilobate ; very gibbous in front, and depressed towards the hinge-line; margin undulating, semi-oval ; 
ventral valve concave; hinge-line extended ; fine and equally radiating strive, partaking of the curvature 
of the surface of the shell. 
Relations and differences.—The outline of this shell is much more undulating, shell more gibbous and 
broader and more distinctly trilobate than the deltoidea. 
It oceurs in the shell-beds, F. 3 a, near the Agency, on Turkey River, Iowa. 
STROPHODONTA OF HALL. 
Generic character.—This genus, established by Hall, is intermediate between the Leptena and Pro- 
ductus. In general appearance it resembles most the Leptena, but has neither aperture nor deltidium ; 
hinge-line is straight, as in Leptzna, but the area forms a trough, and has a toothed or crenulated struc- 
ture; internal structure similar to that of the Productus. 
It is probable that all, or almost all, the Leptzna-shaped fossil shells of the limestones of Iowa of 
Devonian date have the peculiar structure belonging to Strophodonta. 
STROPHODONTA PARVA. (N. 8S.) 
(Tab. III. a, fig. 9.) 
Specific character.—Shell about half an inch wide ; crescent-shaped ; dorsal valve moderately convex ; 
ventral, concave ; surface of both valves finely ribbed, with twenty to twenty-three ribs. 
From the shell-beds of New Buffalo, of the age of the Hamilton Group of New York. 
