NATURAL SCIENCES OF PHILADELPHIA. 167 



be more properly an aberrant Agaricocrinus than a true Dorycrinus. Its arm 

 bases, however, or rather the brachial pieces, have not the breadth and stout- 

 ness seen even in the most aberrant species of the former group, such as Agar, 

 corniculus (= Act. corniculus, Hall), and from their appearance there is little 

 room for doubting that it had two slender arms from each arm opening, in- 

 stead of a single stout one as in Agaricocrinus, which, so far as we are aware, 

 never has more than three arm openings to each posterior ray and two or three 

 to each of the others. It is the only species we have ever seen of the Dorycrinus 

 group with the peculiar sculpturing of its body plates already mentioned. This 

 sculpturing, however, is very different from that seen on Agaricocrinus cornic- 

 iilus, which the species most nearly resembles in several respects, being a 

 peculiar pitting of the whole surface of each individual plate, with a few larger 

 marginal indentations. Its greater number of arm openings (four to each pos- 

 terior ray, and three to the anterior one, instead of two to each all around) 

 would alone at once distinguish it from that species, even in specimens with- 

 out the arms. 



Locality and position. Lower bed of Burlington Limestone, Burlington, Iowa. 

 Lower Carboniferous. No. 150 of Mr. Wachsmuth's collection. 



Genus AGARICOCRINUS, Troost. 

 Agaricocrinus nodoscs, M. and W. 



Body, without the arms, having a truncato-suborbicular general outline, be- 

 ing convex above and broadly truncated below; under side moderately con- 

 cave out to the second radial pieces inclusive. Base small, impressed deeper 

 than the general concavity of the under side, and entirely hidden by the col- 

 umn. First radial pieces extending out horizontally from the end of the col- 

 umn, and exposing a flat hexagonal surface nearly twice as wide as long. 

 Second radials nearly as large as the first, a little wider than long, and pre- 

 senting the usual quadrangular form. Third radials tumid, or projecting dis- 

 tinctly beyond the surface of the second and first; wider than long, larger 

 than the second, and pentagonal or hexagonal in form ; each bearing on its 

 outer sloping sides two series of tumid, stout alternating brachial pieces, di- 

 rected horizontally outward, and in all but the two posterior rays, forming the 

 base of two stout arms. In the posterior rays, intermediate brachial pieces are 

 intercalated between the others so as to give origin in each of these rays to 

 three arms, thus making twelve arms to the entire series. 



First anal piece about as wide as long, heptagonal in form, with a fiat sur- 

 face entirely included within tlie concavity of the under side, supporting in the 

 next range three pieces, which are longer than v/ide, and curve up so as lo form 

 a part of the outer wall, but are not included within the concavity of the under 

 surface. (_)f these the lateral two have a general oval outline, with eight or 

 nine sides and a tumid surface, while the middle one is hexagonal, moderately 

 convex, and much narrower at tlie inner than the outer end. Above these are 

 three other smaller pieces, connecting with the vault. First interradial pieces 

 about once and a half as long as wide, M'ith nine sides, the inner half being 

 flat and included within the concavity, of the lower side, and the outer tumid. 

 Connecting with the outer end of each of these are two elongated narrow- 

 pieces in the second range, which are usually tumid at the lower end, and ex- 

 tend up between the brachial pieces, to connect with the vault. Arms un- 

 known. 



Vault composed of irregular, unequal, tumid larger and smaller pieces. Of 

 the larger, more prominent pieces, one is situated over each ray, and another 

 at tlie middle; while a series of four or five somewhat smaller pieces immedi- 

 ately surround the anterior and lateral margins of the middle one. The inter- 

 mediate spaces are occupied by much smaller and less prominent pieces. 

 Opening nearly over the posterior side and penetrating a very prominent thick- 

 ened ridge, which extends from the middle to the anal side, and is composed 

 of comparatively large pieces for this part, 



1869.] 



