70 PROCEEDINGS OF THE ACADEMY OF 



slightly contracted at the top. Base nearly flat, or presenting a shallow dish- 

 shape, sub-circular outline ; facet for attachment of the column very small. 

 First radial plates generally slightly longer than wide, and nearly quadrangu- 

 lar in form, comparatively moderately thick ; sinus in the upper margin of each, 

 for the reception of the second radials, very shallow, and about half as wide 

 as the upper margin. Anal plate wider below than any of the first radials, 

 but narrowing upward ; provided with a very obscure angle at the middle of 

 the under side, so as to present a sub-pentagonal outline. (Arms and vault 

 unknown.) 



Surface ornamented with comparatively strong, rounded costae, wider than 

 the furrows between. On the base these are arranged in three divaricating 

 series, the lateral costae being parallel to the lateral margins, and the diver- 

 gence upward. On the radial and anal plates there are 7 or 8 of these costce 

 which run nearly vertically and parallel, the lateral ones, however, converging 

 above, so as to leave small triangular spaces on the superior lateral corners, 

 on which there are a few short costs not properly connected with the others. 



Height of body, 0-30 inch ; breadth, 0-37 inch. Cost<e on radial plates, six 

 or seven in the space of 0-20 inch. 



In the coarseness of its costaj this species is nearest like D. striatus, of 

 Owen and Shumard, but it differs in having its costse rather smaller, more 

 rounded and separated by furrows, distinctly smaller than the costae them- 

 selves, which are also without the numerous little asperities seen on those of 

 D. s'riatus. It is also a smaller, shorter species, with a much more depressed 

 or nearly flat base. 



Locality and Position. Upper division of the Burlington group at Burling- 

 ton, Iowa. Mr. Wachsmuth's collection. 



Genus ERISOCRINUS, M. and W. 1865. 



This genus was originally proposed by us for the reception of two A'ery 

 similar forms, one of which, from the upper part of the Coal-Measures of Il- 

 linois, we called E. typus, and the other, from the same horizon in Nebraska, 

 we called E. Nebrascensis. The specimens then known consisted only of the 

 body up to the summit of the first radials. This part of these forms is sub- 

 hemispherical in outline, being rounded below, and evenly truncated above, 

 with five minute, or very small basal pieces, surrounded by, and alternating 

 with, somewhat larger subradials, which in their turn alternate with, and sup- 

 port, five larger, thick first radials, with articulating facets occupying their 

 entire breadth above for the reception of the next range of radials. These 

 radials being in contact with each other all around, leave no spaces for anal 

 or interradial pieces. All the specimens then known had lost the arms, but 

 those of other species now before us are seen to be simple from their origin 

 on the second radial pieces, and each composed of a single series of trans- 

 versely oblong pieces. 



Subsequently another species was found in the same beds in Illinois, pre- 

 senting an obconic form of body, with a protuberent base, and we were so 

 much impressed with its resemblance to an East Indian Carboniferous type 

 described by Dr. de Koninck, under the name Philocrinus, in 1863, that we 

 were led to think our genus not distinct, and his name having priority of date 

 we referred the two forms we had first described to it.* In doing this, how- 



* Our later comparisons of other specimens have led to the conclusion that these are 

 only varieties of one species. Good specimens of a form described by us in the Proceedings 

 for Aug. 1865, from a number of detached plates, under the name E. tuherculatus, also show 

 that it does not belong to this genus, as it has a large oblong subanal, and a true anal 

 piece, resting on the upper truncated edge of one of the subradials. Hence, although 

 it agrees exactly in all its other known parts with Erisorrinus, it cannot properly be re- 

 tained in that genus, but would brlniig to Cyatlincrinus, giving that group the limits gen- 

 erally admitted. It is not a typical Ci/at/nirriniis, however, but nearer the group BanjcriJius, 

 and yet differs from the typical forms of that group, in Iiaving its second radials as wide 

 as the lirst, and articulating by broad transversely fin-rowed facets, instead of merely 

 resting in comparatively small sinuses in the upper edge of the latter. 



[April 



