NO. 1846. OX CERTAIN ELEUTHEROZOIC PELMATOZOA—KIRK. 45 



instances features are to be observed not to be noted in the case of 

 Glyptocrinus. Although capable of attaching and detaching them- 

 selves at will, it apparently was not unusual for the crinoid to remain 

 in any given location for a considerable period of time. As a result 

 it frequently happens that we find the coiled and supporting columns 

 fused together by a secondary deposit of stereom. In such cases it is 

 no uncommon thing to find the sutures of the attached columns com- 

 pletely obliterated. The supporting stem is as a rule somewhat 

 enlarged in the region where it is inclosed. In many cases it appears 

 that the crinoid which had coiled itself about the other column, 

 voluntarily detached itself prior to the death of the supporting organ- 

 ism. In other instances the fracture of the two columns appears 

 equally sharp and indicates a simultaneous disruption. 



From the wide geological range of this structure we may hold that 

 many crinoids, particularly in their young stages, attached themselves 

 by wrapping the prehensile distal portion of their columns about some 

 extraneous object, preferably other crinoid stems. In many, per- 

 haps in most cases, there was a resultant fusion of the two stems. 

 Still later, the crinoid became detached and perhaps led a free exist- 

 ence. In some instances observed the large size of the spirally wound 

 column, and the fact that it does not become tenuous in its distal 

 portion points to the conclusion that this mode of attachment was 

 assumed by fairly adult individuals after a period of freedom. 



Mastigocrinus. — In the case of Mastigocrinus loreus Bather (1892, 

 p. 200, pi. 11, fig. 3) describes and figures a specimen in which the 

 stem is comparatively short, and smoothly rounded off at its distal 

 extremity. It is to be noted in this individual that barring a slight 

 tapering in its proximal portion, the stem is of notably uniform 

 diameter. Considering the splendid preservation of the specimen 

 there would seem to be no explanation for this termination other 

 than that it is a normal feature, and one acquired durmg the life of 

 the organism. 



Calceocrinus. — Bather (1893, p. 75) cites the case of a Calceocrinus 

 interpres from the Silurian of Sweden which apparently had no per- 

 manent distal attachment. The column in this specimen is 44 mm. 

 in length. In the distal portion of the stem the ossicles diminish 

 gradually in diameter. The last three columnals taper off abruptly 

 "so that the stem looks very like a common earthworm." It is 

 evident that we have here a case of complete detachment of the 

 organism, which is all the more remarkable when one considers the 

 extraordinary structure of the crinoid involved. As Bather says, it 

 is scarcely safe to assume that such detachment is normal to this 

 genus. If it were capable of being maintained in the case of one 

 specimen there is no good reason why it should not be assumed by 

 other individuals, however. 



