164 PROCEEDINGS OP THE ACADEMY OP 



comparatively stout. Column near the base nearly or quite round, and com- 

 posed of very thin pieces. Surface smooth. 



Length of body to summit of first radial pieces 0-12 inch ; breadth of do. 

 0-12 inch. Length of arm about 0-30 inch; thickness of column, 0-02 inch. 



This very small species, differs remarkably from all the others with which 

 we are acquainted, resembling it in other respects, not only in its small size, 

 but in having two minute radial pieces in each ray, above the larger first radial 

 piece, making three radials to each ray. 



Locality and position. Pope County, Illinois. Chester division of Subcarbo- 

 niferous Series. 



Genus ACTINOCRINUS, Miller, 1821. 



Subgenus ALLOPROSALLOCRINUS, Lyon & Casseday, 1860. 



Actinocrinos (Alloprosallocrinus) euconds, M. & W. 



Body having the form of the subgenus remarkably well developed, being 

 perfectly flat or slightly concave below the arm bases, and regularly conical 

 above, where it terminates in a rather slender central proboscis. Base very 

 small, with a round, deep, conical depression for the reception of the column, 

 occupying almost its entire area, and surrounded by a narrow, slightly pro- 

 jecting ring-like margin. Radial, interradial, anal and first brachial pieces, 

 all extending out horizontally from the base. First radial pieces hexagonal 

 and about twice as wide as long. Second radials transversely oblong, and 

 rather, smaller than the first. Third radials a little larger than the second, 

 pentagonal or hexagonal in form, and each supporting on its superior (more 

 properly outer) sloping sides two slightly larger secondary radials, each of 

 which is succeeded by another, and the latter each by two brachial pieces, 

 making four arms to each of two rays seen, or twenty to the entire series, if 

 the others have the same number. First interradial pieces larger than any of 

 the radials, heptagonal or octagonal, and supporting two smaller pieces in the 

 next range, beyond which are two others, making altogether five pieces in the 

 only interradial area we have been able to make out clearly. Anal pieces un- 

 known. 



Vault regularly conical, with slightly eonvex slopes, and armed around the 

 middle with two or three rows of irregularly disposed, short, conical spines, 

 or spine-like tubercles. Proboscis slender and apparently not inclined to 

 either side. 



Surface smooth, or indistinctly granulose ; sutures very close fitting and 

 difficult to see. Arm bases forming an almost continuous series (being but 

 very slightly interrupted at the anal and interradial spaces) around the base 

 of the abruptly truncated conical body. Column unknown. 



Height to base of proboscis, about 0.70 inch ; breadth, 1.13 inches. 



This species is remarkable for its conical form, being almost perfectly flat, or 

 a little concave below the horizon of the arm bases, and rising with slightly 

 convex slopes above, to the base of the proboscis. Hence the whole of the 

 cavity occupied by the viscera of the animal corresponds to the dome only of 

 species of the usual form of Actinocrinus. For the group to which it belongs. 

 Messrs. Lyon & Casseday proposed the name Alloprosallocrinus in 1860, and 

 Dr. Troost had proposed for it the name Conocrinus, in a list published without 

 a description in 1850. 



Since the above was in type, a more careful comparison with Lyon & Casse- 

 day's description of their A. conicus leads us to suspect that our crinoid may 

 be identical with their species. Still we do not feel satisfied that this is the 

 case, particularly as they describe the columnar facet as involving the basal 

 and part of the surrounding range of pieces ; while it is very small in our 

 crinoid, not even covering the small basal pieces. In addition to this, our 

 specimens seem to show the bases of a more numerous series of arms. 



[Aug. 



