168 PROCEEDINGS OF THE ACADEMY OP 



Surface of all the plates, including those of the vault, regularly granular. 

 Column of moderate size, round, and composed near the base of alternately 

 thicker and thinner pieces, with radiately striated surfaces, and perforated by 

 a very small nearly rounded central canal. 



Height of body to top of vault, 088 inch ; breadth, including three brachial 

 pieces on each side, 1-13 inches; breadth of concavity of underside, 0-57 inch; 

 thickness of column 0-40 inch from base, O-lTinch. 



This species differs from all the others yet known from the Burlington group, 

 in having three arms to each posterior ray. It is most nearly allied to .-1. buL' 

 latus. Hall, a single individual of which, out of a considerable number in Mr. 

 Waclismuth's collection, has abnormally three arms in one of the posterior rays 

 all the others having two to each ray all around. It differs also from all of these, 

 however, as well as from the original type now before us, in having the conca- 

 vity of the under side less dee]), and all the pieces surrounding it more tumid, 

 wliile the form and proportions of its l)ody pieces are different, its anal region 

 much more protuberant, and its vault pieces less rounded and swelled. Its 

 surface is also more coarsely granular. 



Locality and position. Highest part of the upper bed of the Burlington group 

 at Burlington, Iowa. Lower Carboniferous. No. 14'5 of Mr. Wachsmuth's col- 

 lection. 



Genus PLATYCRINITES, Miller. 



Platycrinites tenctibrachiatus, M. and W. 



Body rather small, subglobose, being somewhat wider than high. Base 

 shallow, or dish shaped, with a subpentagonal outline and a ratlier broad 

 shallow concavity below, nearly twice as wide as the rather small round facet 

 for the attachment of the column. First radial pieces a little wider than high, 

 having a general quadrangular form, but with tlie superior lateral angles 

 slightly truncated for the reception of the interradial pieces, and the lower sides 

 a little convex in outline; sinus in the upper side of each equaling about half 

 its breadth, and extending down on the outer side about one-third to one-fourth 

 its length. Sutures channeled by the beveling of the edges of the plates. 

 Second radial pieces very small, wider than long, triagonal in form, and wedg- 

 ing out on each side so as to allow the first brachial pieces to come in contact 

 with the first radials at the lateral edges of the sinuses in the same. 



First divisions of the rays, from their origin on the second radial pieces, 

 each round and composed of a single series of somewhat wedge shaped pieces 

 to the fourth piece, which has a pentagonal outline and gives origin to two 

 divisions, the inner one of which is smaller than the other and without farther 

 bifurcations, being a simple arm, composed below, for some little distance, of 

 a single series of wedge formed pieces, beyond which it passes gradually into 

 a double series of alternating pieces, while the outer division bifurcates on the 

 second piece, its outer subdivision remaining simple like the inner of the first 

 divisions, already described, and its inner division bifurcates again on the 

 fourth pieces, forming two arms like the others, thus making four arms to 

 each of the two main divisions of each ray, or forty arms to the entire series, 

 all of which are long, slender, and without spines or other asperities. PinnuUe, 

 or so-called tentacles, slender, rather crowded, and composed of joints that 

 are longer than wide and deeply furrowed within. 



Surface of body plates marked with small rough ridges, which on the first 

 radial pieces run parallel to the lower and lateral margins, with more or less 

 irregularly disposed granules on the central region, sometimes showing a 

 tendency to radiate from the sinuses for the second radial pieces. 



Height of body, 0-30 inch ; breadth of same, 0-50 inch ; length of arms, meas- 

 uring from the first divisions on the second primary radials, about 1-50 inch . 

 do. to first bifurcation above, 0-22 inch ; breadth of each individual arm above 

 all the bifurcations, 0-05 inch. 



[July. 



