154 SYNOPTIC COLLECTION. 



The most complex Cyathocrinoid must have passed 

 through a stage in early life when it closely resembled 

 Haplocrinus. Cyathocrinus (PI. 269, figs, i-io; No. 270), 

 is attached by a round stem (No. 270, C. multibrachiatus 

 L. & C.; PI. 269, fig. 2) which never developed branches 

 or cirri (see figs. 1,4). Small underbasal plates, five in 

 number, are found (not seen in No. 270, but figured in PI. 

 269, fig. i, young stage, and fig. 3, plates of body sepa- 

 rated). The underbasals are characteristic of Palaeozoic 

 Crinoids, as we have already said, but do not occur among 

 recent adult forms. 1 Fig. 4 represents the adult in which 

 the plates of the body are not so distinctly seen as in the 

 young (fig. i). Above the underbasals are five basals and 

 five radials with a small anal plate. These are not seen 

 in No. 270, but are shown in figs, i, 3. The basals de- 

 velop very early in the young and have nearly reached 

 their full size when the radials are still small. 2 An anal 

 tube (ventral sac, Wachsmuth and Springer) rose from 

 the ventral surface, which was short and covered by plates 

 (figs, i, 4, 5). 



The ambulacral grooves run out from the mouth, across 

 the ventral surface, and are concealed by small, irregular 

 covering plates (fig. 6 ; fig. 7, ventral surface with ambu- 

 lacrals and covering plates removed). When the Crinoid 

 was alive, these covering plates could open (fig. 8) , and 

 thus food could pass through the grooves (figs. 7, 9) to 

 the mouth, after which the covering plates were again 

 closed, as seen in fig. 10. 



A few long, slender arms are sent off from the radials, 

 which in some species fork many times forming armlets, 

 but which are without pinnules (figs. 1,4). 



The interesting discovery was made by Wachsmuth 

 and Springer 3 that what had been considered hitherto as 



1 Chall. Rep., Zool., XI, part 32, 1884, p. 152. 

 2 Chall. Rep., loc. cit., p. 169. 



3 Transition forms in Crinoids and description of five new species, 

 Proc. Acad. Nat. Sci. Phila., 1878, p. 256. 



