The Galena and Maquoketa Series. — Sarde.sori. 103 
found in beds No. 12 and 13 of the Maquoketa series. Those refen-ed to 
in the original description of O. einacerata Hall, as found in Illinois and 
Iowa, are of a different species that is found with Telliiiomya fecnnda 
Hall, in bed No. 11. 
Orthis emacerata Hall* (O. niacrior Sardeson) are semicircular shells, 
broadest near the hinge line, and with the margin rounded off narrowly 
at the ends of the hinge. Their breadth is one-fourth or less greater 
than their length. The ventral valve is convex, the dorsal one nearly 
plane, but the convexity is often irregularly increased in both valves of 
senile individuals, and those marked by many concentric lines. Near 
the beak of the ventral valve the single median plication is prominent 
and thence the median fold that expands towards the anterior margin, 
coincides with the median fascicle of plications. On the dorsal valve a 
corresponding depression obtains, which is, however, in some, relatively 
deeper than the opposite fold, so that the anterior margin is straight- 
ened. The ventral valve has the beak short, acute and slightly curved, 
the area about twice as high as that of the dorsal valve, and divided by 
equilaterally triangular foramen. The cardinal process was a little small 
and was tripartate, but in poor preservation it is cleft, the middle por- 
tion being wanting. The dorsal median septum and the crura are both 
light in accord with the thinness of the valves, but the dorsal muscle 
scars are deeply marked. The anterior pair of them are the larger. On 
the ventral valve the muscle scar area is well defined, — narrowest on 
thickened shells, when also the vascular sinuses and ovarian spaces are 
unusually well outlined. 
The plication of O/'^/n's emacerata YiaW, resembles that of large, and 
hence, flat specimens of O. rogata Sardeson. The plications are often 
graded in size, the first formed then being largest. The sui-face is with- 
out the minute transverse marking that is seen on O. mnltisecta Meek, 
et al., in all my specimens, but few specimens of O. rogata Sardeson, 
and O. eorpulenta Sardeson, have it well preserved, the same being eas- 
ily defaced. 
The Cincinnati sijecimens average larger than those from Minnesota 
(beds 12, 1.3), but at Nye, Wisconsin (bed 14), are yet smaller and nar- 
rower ones that may be a distinct variety. 
Certainly the similarity between O. emacerata Hall, and large, and 
hence flat specimens of O. rogata Sardeson, is very great, and one can 
not doubt that the same is indicative of a close relationship between 
them. The geologic data would permit of the theory that the latter 
is the immediate parent species, O. emacerata having de.oconded from 
well favored, like O. multisecta from dwarfed individuals of O. rogata. 
The theory might be given consideration were we able to explain the 
want of minuter surface ornamentation on O. emace)-ata, and were it 
not that the Trenton of Trenton Falls, New York, yields this type of O. 
testudinaria. The relationship may be concluded to have been geolog- 
*Specimens from the original lot have Vjeen obtained for examination 
through kindness of Prof. R. P. Whitfield, curator of the Geological De- 
partment of the American Museum of J^atural History, New V(jrk city. 
