CALAMOCRINUS DIOMED.E. 63 



The great increase in the dimension of the colunm of certain Crinoids 

 at its upper extremity, forming as it were a j'l'olongation of the cup of 

 the Crinoid gradually passing into the stem, is an interesting structural 

 character. It dates back to some of the Cystideans, in wliich the upper 

 extremity of the stem is far more closely connected with the plates of the 

 cup than is the case in Crinoids proper. 



In the Cystidean stems figured by Hall in the Palaeontology of New 

 York, there are also many cases to show that young joints are interca- 

 lated in the upper part of the stem between the older ones. 



How ditlerent the stem of some of the Cystideans is from that of the 

 other Crinoids is best illustrated by the structure of the upper part of the 

 stem of Dendrocystites,* in which the plates of the test form a poucli which 

 gradually passes into a regular cri-noidal stem. Neumayerf considers this 

 type of stem as the primordial form. 



The base of the column of Cystids is remarkable for its peculiar structure 

 and shape. The upper part, where new joints appear, consists of joints 

 quite similar to those of the true Crinoids, but the lower part is somewhat 

 club-shaped (Hall, Palreontol. of New York, Vol. III. Plate 7. Figs. 5, 6, 

 14-16, 20-22). The axial cavity of this part of the column is large. 



That the pentagonal stems hold a definite relation to the calyx has been 

 clearly shown by Wachsmuth and Springer,| and goes far to prove that 

 the stems must originally have had a far more intimate connection with 

 the calyx than its representatives of to-day have; and the fact that in a 

 number of palaeozoic Crinoids the axial canal is very wide compared with 

 that of recent types seems to indicate an additional function to that of 

 the axial canal, which, as Neumaj'er suggests, we cannot explain from 

 the recent representatives. 



The large size of the axial opening in Mariacriiuis would seem to indicate 

 other u.ses for it tlian merely the protection of the axial cords. See Hall, 

 Palseontol. of N. Y., Vol. III. Plate 3 B. Hall's Figure 2 indicates a commu- 

 nication between the main axial cavity of the column and tlie rootlets. 



* Barraiule, Sj-st. Sil., Vol. VII. Plates 26 and 27. Billings has also given very fine figures of 

 stems of Cystideans (Plumocystites, Canad. Geol. Survey, Decade 3, Plate I.), showing the great size 

 of the base of the stem. 



t Is not the loss of the stem in the Comatulae, as suggested by Neumayer, foreshadowed already 

 among Cystideans, in which many of them have a stem which gi'adually tapers, so that it could be of 

 use for oidy the sliglitest possible attachment, and finally frequently is present as a mere shrivelled 

 wart-like appendage ? 



t Proc. .-^cad. Nat. Sci. Phila.. 188.i, p. 229. 



