358 PROCEEDINGS OF THE ACADEMY OF [1879. 



transverse plates, with parallel sutures, as in the two species of 

 Gromyocrinus from Russia. We have an example in a specimen 

 from Kentucky, which we owe to the kindness of Prof. Wetherhy, 

 evidently Eupachycrinus formosus (Zeacrinus formosus Worth.), 

 which in every other respect is so closely allied to Eupachycrinus 

 spartarius S. A. Miller (which has two rows of alternating arm- 

 pieces), that the two cannot be separated unless the arms are 

 preserved; while, on the other hand, it is almost identical with 

 Trautschold's Cromyocrinus geminatus. This is sufficient to 

 show the impracticability of subdividing Eupachyocrinus, and we 

 are forced to consider Gromyocrinus as a synonym. 



It is certainly pertinent to inquire how it is possible that the 

 same differences in the structure of these Crinoids are in some 

 cases of generic, and in others only of specific importance. We 

 think the question can be answered without much speculating. 

 In a paper, "Transition Forms in Crinoids," Proc. Acad. Nat. 

 Sci. Phila., 1878, p. '224, we have endeavored to prove that ex- 

 travagant forms ai*e of short duration ; that many genera, before 

 they become extinct, attain extreme proportions or become extra- 

 ordinarily developed in certain parts of the body. Such was the 

 case with Hydreionocrinus with regard to the ventral sac, which 

 was developed to its farthest extreme iu size and proportions. In 

 Eupachycrinus the opposite extreme is reached, the same organ 

 being reduced to almost nothing, making it almost doubtful 

 whether the genus ought to be placed with the Gyathocrinidce at 

 all; although we cannot, with our present knowledge, separate it 

 from this family. This form was one of its very latest repre- 

 sentatives, which evidently struggled through under great diffi- 

 culties, and which by degrees accommodated itself to the great 

 changes which took place about the close of the Carboniferous 

 Age. All the peculiarities which are expressed in the genus, the 

 differentiations which distinguish the species, point toward and 

 foreshadow Encrinus. We observe this in the form and con- 

 struction of the calyx; in the number, size, and arrangement of 

 the arms; in the mode of articulation, and in the general aspect. 

 The two mainly differ in the absence of anal plates in Encrinus; 

 but here again we find in. the species of Eupachycrinus, to which 

 we alluded above and which are restricted to the Coal Measures, 

 the forerunners of Erisocrinus and Stemmatocrinus of the same 

 horizon, which are the prophetic types, if not congenera, of the 



