WHITE. ] CARBONIFEROUS FOSSILS. 135 
Genus SPIRIFER Sowerby. 
SPIRIFER AGELAIUS Meek. 
Plate 34, figs. 10 a@ and b. 
Spirifer triradialis Phillips? Meek, 1873, An. Rep. U.S. Geol. Sur. Terr. for 1872, p. 470. 
Spirifer agelaius Meek ib., in a foot-note. 
Shell small, somewhat inflated, breadth a little greater than the length} 
hinge margin never longer than the greatest breadth of the shell, and 
usually shorter; anterior and lateral margins, except » little straight- 
ening at the front, forming an approximately regular curve, which com- 
prises more than a semicircle. ; 
Ventral valve somewhat more convex than the dorsal; umbo promi- 
nent, and from it the sides of the valve slope by a gentle convexity to 
the margins, the convexity being less at the sides than at the front; 
beak prominent, curved, and projecting backward over the hinge margin; 
area rather small, moderately high, arched, its lateral margins not well 
defined from the sides of the valve; mesial sinus rather narrow, but 
traceable from the front to the umbo, and bordered on each side 
by a moderately large, prominent, rounded rib, rather shallow, and hav- 
ing a faint ridge along its middle, which is perceptible only near the 
front, or it is only a little fattened at the bottom; upon each side of the 
sinus there are three and sometimes four ribs, which are smaller than 
the two that border the sinus, and which successively diminish in size 
and distinctness outwards, so that the fourth one is never very distinct. 
Dorsal valve nearly regularly convex; beak not prominent, a little 
incurved, and projecting very slightly, if at all, over the hinge margin ; 
mesial lobe distinct, broader than the sinus of the other valve, with a 
faint median groove, or the lobe is a little flattened along its middle, 
bounded by grooves which are a little deeper than those which sepa- 
rate the ribs from each other; ribs three or four on each side of the 
mesial lobe, answering in character respectively to those of the other 
valve. Besides the ribs, the markings of the surface are only the usual 
concentric lines of growth. 
Length of the largest dorsal valve in the collection, 64 millimeters ; 
breadth of the same, 9 millimeters. All the other examples in the col- 
lection, which are somewhat numerous, are smaller. 
This species is reported from the Carboniferous strata of “Old 
Baldy” mountain, near Virginia City, Mont. The following are Mr. 
Meek’s remarks upon it: 
“A very abundant, gregarious little shell, closely resembling 8. tri- 
radialis (Phillips) var. sexradialis, as illustrated by Mz. Davidson, ex- 
cepting that the largest of hundreds of specimens are less than one- 
fourth the size of well-developed individuals of that form. It also 
differs in being constantly wider than long, instead of the reverse, and 
in having the back of its ventral valve always proportionally shorter ; 
while it shows a faint sulcus along the mesial fold towards the front, 
and a corresponding very slight ridge in the bottom of the sinus of the 
dorsal valve. I think it probably a new species. If so, it may be 
called 8. agelaius.” 
The differences between this shell and the S. triradialis var. sexra- 
dialis of Davidson are evidently incompatible with specific identity, and 
( therefore treat it in this article as a distinct species under the specific 
uame proposed by Mr. Meek. 
