NATURAL SCIENCES OF PHILADELPHIA. 157 



ACTINOCRINITES. Section {b). 

 AcTiNOCRiNiTES LONGUS, M. and W. 



Body rather elongate-obconic below the arms, the sides expanding gradu- 

 ally, with a moderately convex outline from the base to the tertiary radial 

 pieces, which, with the brachial pieces, curve very slightly outward. Base 

 about twice and a half as wide as high, not thickened or expanded below, 

 and but very slightly notched at the sutures; facet for the reception of the 

 column large and moderately concave, with a rather large central perforation. 

 First radials comparatively large, very nearly or quite as long as wide. 

 Second radials scarcely half as large as the first, about as wide as long, 

 quadrangular, pentagonal or unequally six-sided. Third radials of about the 

 same size as the second, pentagonal, hexagonal, or heptagonal, and each 

 bearing on its superior sloping sides two secondary radials of near its own 

 size, each of which supports, on its outer sloping upper side, brachial pieces, 

 leading to an arm, and on its inner side, above, a small tertiary radial giving 

 origin to two arms, thus making three arms to each main division, and six to 

 each ray, or thirty to the entire series. (Arms unknown.) 



Anal plates five or six, the first being of the same size as the smaller first 

 radials, hexagonal in form, and a little longer than wide ; second anals two, 

 about two-thirds as large as the first, and irregularly heptagonal or octago- 

 nal ; above these there are two smaller pieces in the third range, and one 

 or two still smaller pieces above the latter, the upper one being barely large 

 enough to separate the posterior lateral brachial pieces of the two posterior 

 rays. First interradial pieces about half as large as the first radials, heptag^o- 

 nal, and supporting two smaller pieces in the second range, above which there 

 are one or two still smaller pieces in the third, and a minute piece over the 

 latter, wedged in between the brachial pieces. In each interaxillary space 

 there are usually two intercalated pieces, the lower of which is sometimes as 

 large as one of the tertiary radials, while the upper is very small, and wedged 

 in between the brachial pieces. 



Vault conical, and nearly three-fourths as high as the body below the 

 arms ; composed of irregular pieces of moderate size, some of which project 

 in the form of small pointed nodes or short spines, passing gradually into a 

 rather large subcentral proboscis. 



Surface of all the body plates rather distinctly convex, but not properly tumid, 

 and showing but the faintest traces of an effort to form, on some of the small- 

 er pieces, an obscure radiating ridge near each side. In most cases, how- 

 ever, these are entirely obsolete, and the plate seems to be merely evenly 

 convex. 



Height of body to arm bases, \-2) inch; breadth of do. at arm bases, 1-40 

 inch ; height of vault, about 0-80 inch. 



In the structure of its body, as well as in its arm formula, this species 

 agrees with Actinocrinus clavus^ of Hall. It differs, however, greatly in form, 

 as well as in the surface characters of its body plates, being rather elongate 

 obconical below the arms, instead of " very broadly subturbinated, and 

 spreading more rapidly above the third radial plates;" while its body plates 

 are merely convex, instead of being " elevated into strong angular nodes, some 

 sometimes marked by low ridges on the lower part," and by "strong angular 

 ridges " on the upper part. 



Its elevated conical vault, passing gradually into the nearly central pro- 

 boscis, and narrow obconic body below the arms, give it a peculiar fusiform 

 outline. In the nature of its vault it resembles quite nearly A. coslatus of 

 Hall, from which, however, it differs widely in other respects. 



Locality and position. — Lower beds Burlington group of Lower Carbonife- 

 rous, Burlington, Iowa. Mr. Wachsmuth's collection. 



1869.] 



