I LLAMOCRINUS DIOMED l 



The ureal increase in the dimension of the column of certain Crinoids 

 at iis upper extremity, forming as ii were a prolongation of the cup of 

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



character. Ii dates back to s i of the Cystideans, in which 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 thai young joints are interca- 

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



How different the Btem of some of the Cystideans is from thai of the 

 other Crinoids is best illustrated by the .structure of the upper pari of the 

 stem of Dendrocystites,* in which the plates of the tesi form a pouch which 

 gradually passes into a regular crmoidal 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 pari is somewhal 

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

 14-10. 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 thai 

 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 paUvozoic 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 Neumayer suggests, we cannot explain from 

 the recent representatives. 



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

 other uses for it than merely the protection of the axial cords. See Hall. 

 Palaeontol. 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 the rootlets. 



* Barramle, Syst. Sil., Vol. VII. Plates 26 and 27. Billings has also given very fine figures of 

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

 of the base of the stem. 



f 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 gradually tapers, so that it could be of 

 use for only the slightest possible attachment, and finally frequently is present as a mere shrivelled 

 wart-like appendage ? 



i Proc. Acad. Nat. Sci. Phila.. 1SS."., p. 229. 



