278 ECHINODEEMATA. 



upright lamellae that support the polygonal plates of the upper side, and often leave then- 

 impression, like the radiations of a star, upon the object to which it was attached. The 

 stalk rises from the central depressed area, and consists, at first, of Interlocking plates, 

 but, afterward, of circular ones, like those of a crinoid column, and finally tapers to a 

 point. It was flexible and perforated with a longitudinal channel, though the perforation 

 has not been satisfactorily ascertained at the upper terminating point. 



ORDER MYELODACTYLOIDEA, n. ord. 



This division of the fossil Eohinodermata is established as follows : 

 Body free, discoidal, and possessed of an internal radiating system of pores, which 

 increase, by division, from the center to a tubular channel in the circular margin or sur- 

 rounding coil. There are two families referred to this order, the Myelodactylidse and 

 the Cyclocystoididse. In the former, the radiating and circular systems become com- 

 plicated, by the connection, between succeeding coils and through the flattened connect- 

 ing finger-like processes ; in the latter, the arrangement is more simple, as the interior 

 ■ radiations connect with a single marginal circular system. The external form and in- 

 ternal structure are so essentially distinct from other well defined orders, that the tech- 

 nical names, used in description, have no ascertained application. That is, we can not 

 intelligently apply the words calyx, ambulacra, arm, etc., to any part of these peculiar 

 organisms. This order h.js been suggested with hesitation, because there still exists a 

 possibility that Myelodactylus belongs, in some manner, to the vault of a crinoid, but 

 the author thinks there is not much probability of such connection. 



FAMILY MYELODACTYLIDvE, n. fam. 

 This family is founded upon the single genus Myelodactylus, and defined as follows : 

 Body free, discoidal, and resembling a coil rolled in the same plane, and covered 

 upon either side by finger-like processes from each succeeding turn overlapping the 

 next inner one. The whorls are composed of a series of plateSj having a tubular channel 

 within, and perforated and finger-like processes upon the .exterior, directed toward the 

 center, and flattened down upon the next inner whorl to which thej' are attached, and 

 form a porous connection from the tubular channel of one whorl to the next inner one. 

 The cast of the pores of the iniier whorl resemble the radiating spokes of a wheel : they 

 are multiplied in connecting the tubular channels of each succeeding whorl, thus making 

 the internal radiating system doubly complicated. The central aperture, if one exists, 

 has not been discovered, and the structure of the terminal end of the anomalous coil is 

 wholly unknown. The internal radiating system of pores may be compared with that 

 of the family Cyclocj^stoididse, and here the .analogy in structure, with other families in 

 the class Eohinodermata, so fr as known, ceases. The terminal end of the coil being 

 unknown has led to the suggestion of the possibility of its having been connected with 

 the vault of a crinoid, but as no genus is known having any such appendage, and some 

 classification seeming desirable, this family has been proposed. 



FAMILY CYCLOCYSTOIDID^E, n. fam. 

 This family is founded upon the single genus Cyclocystoides, and defined as follows : 

 Body free, consisting of a circular disk, and having a margin composed of a series of 

 perforated plates. Within this marginal series the disk is covered with an integument of 

 small plates, except, possibly, a small central aperture. The rim or marginal series 

 contains a tubular channel, making the complete circle, which is connected with the in- 

 terior, by numerous pores, that radiate from the center, and repeatedly bifurcate be- 

 fore reaching it. The inner side of the rim is grooved, for the reception of the internal 

 part of the disk, and the outer side depressed and scarred, either by mammillary eleva- 

 tions or concave depressions, as if for the attachment of ossicular or other processes. 

 The tubular channel is connected with the exterior by minute circular pores which were 

 probably analagous, in their purpose, to the calycine pores in the Cystideaj. 



