NATURAL SCIENCES OF PHILADELPHIA. 151 



of moderate thickness, everj' Hllernate or third one of which projects out 

 distinctly beyond the others. Central canal minute and apparently round. 



Height of body to the top of the first radial pieces, O-IO inch; breadth, 0-31 

 incli ; length of arms, about 1 inch. 



This is another species related to Zeacrinus spinobrachiatus, of Dr. White, but 

 it differs in having decidedly more slender arms below the bifurcations, with 

 the arm pieces, particularly above the first bifurcation, arranged much more in 

 zigzag, and their thicker ends more projecting on each side. It is one of the 

 forms combining some of the characters of Zeacrinus and Scophiocrinus. 



Locality and position. Upper division of the Burlington group, Burlington, 

 Iowa. Lower Carboniferous. No. 323 of Mr. Wachsmuth's collection. 



Zeacrixus serratus, M. and W. 

 Body small, much depressed, or about three times as wide as high, broadly 

 truncated and concave below. Base very small, and nearly or quite concealed 

 by the column in the concavitj' of the under side. Subradials a little tumid, 

 curving abruptly into the" concavitj- of the under side, and extending about 

 half way up the lateral walls of the body ; three or four pentagonal and one or 

 two on the anal side hexagonal (not counting a very obtuse angle doubtless 

 existing at the middle of 'the under side of each). First radials somewhat 

 larger than the subradials, nearly twice as wide as high, and all pentagonal in 

 form, with the upper side equaling the entire breadth. Second radials as wide 

 at the base as the first, and nearly twice as long, each pentagonal in form and 

 supporting two arms, excepting that of the anterior ray, which is quadrangular 

 and supports but a single arm; each with a prominent, well defined, sharp 

 carina extending up the middle, and the dorsal surface on each side of this 

 carina is distinctly concave. Anal pieces arranged in a double alternating series 

 almost exactly as in the last. 



Arms (excepting in the anterior ray) bifurcating first on the sixth piece 

 above their origin on the second radials, the inner division being slightly 

 smaller than the other, and simple to the end, while the outer division bifur- 

 cates again on the seventh piece above, and a third time on the eighth piece 

 above the latter, the inner divisions being all simple. Arm pieces very short, 

 or two or three times as wide as long, and scarcely showing any tendency to 

 assume a wedge shaped outline ; each one with a small pinched or angular 

 projection on the middle of the dorsal side, giving the arms a subcarinated 

 apiiearance ; but these projections are not continuous, being separated by 

 notches at the sutures between the pieces, and a little inclined upward, so as 

 to impart to the dorsal side of the arms a serrated appearance, as seen in an 

 outline lateral view. Axillary pieces at all the bifurcations of the arms larger 

 than the other arm pieces, and more prominent and angular. 



Surface of body plates merely convex, or somewhat tumid, and without 

 costte or carinte. Column very small, round or subpentagonal, and composed, 

 near the base, of nearly equal rather thin pieces, with a very minute central 

 perforation. Sutures between the first and second radial pieces widely 

 gaping. 



Height of body, 0-07 inch; breadth, about 22 inch ; length of arms, about 

 0-60 inch. 



In several respects this species agrees almost exactly with Z. rar/wsus, of 

 Hall, which has the same proportion?, with its arms bifurcating in exactly the 

 same way, and composed of similar short pieces, showing no tendency to a 

 weilge formed outline. On comparison with the original typical specimen of 

 that species, however, now before us, the species under consideration is found 

 to differ in having its second radial pieces each provided with a sharp, strongly 

 defined mesial carina, and the surface on each side of the carina distinctly 

 coucave, instead of having these pieces merely obtusely rounded. The same 

 or a similar difference is also seen in the arm pieces, each of which is provided 

 with one or more little projections on the dorsal side, instead of being smoothly 



1869.] 



