NATURAL SCIENCES OF PHILADELPHIA. 29 



length of the arms, comparatively rather narrow and Bub-cylindrical below 

 but widening rather gradually upward above to the summit, where n Barea 

 suddenly out all around to about the breadth of the body below, its top bi 

 nearly flat, or much depressed, and composed of small, unequal, convex pi< 

 while each one of the marginal row of these top pieces, all around, extends 

 horizontally outward in the form of a sharp spine about two-thirds as long 

 the entire transverse diameter of the flattened top itself.* Plates forming the 

 sides of the ventral portion, below its flattened spiniferous crown, probablj 

 more or less costated, or sculptured, in perfect examples, but thfe specimen 

 seen is not in a condition to show this, though the usual pores can be seen 

 passing through the sutures between the plates. Surface of body and a 

 apparently smooth. 



Height of body to top of first radials, about 0-18 inch ; breadth of do. 065 

 inch; height to top of ventral portion, including the body, 1-20 inches; 

 breadth of the flattened top of the ventral portion, exclusive of the free mar- 

 ginal spines, about 0-50 inch ; whole breadth across same to the extremities 

 of the spines. 



The form of the body and the arrangement of the anal pieces of this species 

 are very similar to those of cur Z. discus, from the Upper Coal measures, but 

 its under side is more decidedly concave, its first radial pieces proportionally 

 higher, and separated by decidedly deeper sutures. Its subradials are also 

 proportionally smaller. From Z ? mucrospimt*, of McChesney, it is at once 

 distinguished by not having its second radial pieces developed into spines, 

 and by the different structure of its arms. 



Locality and position. Fulton County. Associated with the lowest coal bed of 

 the Illinois Coal-measures. 



* On comparing this Crinoid with Prof, de Koninck's figure of the type of his gen is 

 Hydreionncrinus (H. Woodianus; Bull, de l'Academy Royale de Belgique, 2me serie, tome 

 III, pi. ii), we have been much impressed by the remarkable resemblance of the large 

 ventral extension of its body with its depressed or flattened crown, surrounded by a se- 

 ries of marginal spines directed horizontally outward, to the part in Prof, de Koninck's 

 type supposed by him to be formed by the lateral coalescence of the arms, in such a 

 manner as to form a kind of cylindrical extension of the body upward. In our spi 

 however, there are unquestionably well developed, free arms, independent of this part. 

 It would be such an anomalous structure for a Crinoid belonging to the Cyathoerinidx, ami 

 otherwise so similar to Zeacrinus and Poteriocrinites as Hydreionncrinus is, to have no ti ices 

 of free arms, that we are tempted to make the inquiry, whether Prof, de Koninck's speci- 

 men may not have had its arms broken away and the lower parts of the rays on which 

 they rested accidentally pressed in so as to appear to support the ventral extension; or, 

 in other words, so as to give this part the appearance of being actually composed of the 

 arms themselves united laterally and crowned by a vault? If this upward prolongation 

 of the body was really composed of the arms united laterally, and there were no free 

 arms, with the usual ambulacral openings at their bases, the whole visceral cavity would 

 seem to have been hermetically sealed, excepting perhaps the minute lateral pores we 

 have found to exist in the ventral extension of many analogous forms. Prof, de Koninck 

 distinctly states that he was unable to find any traces of an anal or buccal opening in nis 

 type, and we have been equally unable to find any traces of such openings in any of the 

 numerous specimens of Pnterincrinus, Scaphiocrinus, Zeacrinus, Oxlocrinus, and other analo- 

 gous forms we have seen, that are provided with a similar large ventral extension of the 

 body. But in all these types there are well developed free, arms, with ambulacral openings at t'teir 

 bases. It will be remembered that the genus Bdphcrinus was supposed to have its arms 

 united to form a kind of conical vault, until Muller discovered a species with true free 

 arms independent of this part. 



If Bydreionocrinus really possessed free arms, it would otherwise agree so exactly with 

 Zeacrinus that it would seem to be impossible to separate them even subgenencally: in 



which case Troost's name would probably become a synonym under Bydrewr, rtnus as 



Prof de Koninck's name was, we believe, published a few months earlier than Dr. 

 Troost's It is to be hoped that those who may have an opportunity to examini 

 specimens than those studied by Prof, de Koninck, of the typical species of Bydrtia - 

 nus*wi\\ examine them very carefully to see if some remains of free arms cannot be 

 found. 



* Hndreionocrinusf glnlmlaris. de Kon., seems to us to belong to a distinct genus ne^lya'- 

 lied to Agassizocrinus\ which in some species has its base distinctly divided into five parts. 



1870.] 



