CLARK: CRINOID FAMILY PLICATOCRINIDAE 495 



meet above it in five sharp parallel edges, as do the orals of the 

 stalked young of the macrophreate comatulids. 



3. The calyx is more or less asymmetrical; the two posterior 

 radials may be enlarged, as in Calamocrinus, or there may be a 

 very small basal just to the right of the anal area, as in Hyocrinus. 

 In the young of the comatulids the two posterior radials may be 

 larger than the others, and there is always a radianal, situated 

 more or less to the right hand side of the posterior interradius. 



4. The dorsal cup is very large, entirely enclosing the visceral 

 mass dorsally and laterally; this condition is identical with that 

 found in the young of the comatulids, but only occurs in the adults 

 of the Articulata in the highly aberrant Marsupites. 



5. The plates of the dorsal cup are very thin, entirely lacking 

 the extensive inward calcareous development so characteristic 

 of all the other species of the Articulata; in this the Plicatocrinidae 

 agree with the young of the comatulids, and with the highly 

 aberrant pelagic comatulids Marsupites and Uintacrinus. 



6. Instead of occupying the entire distal edge of the radials as 

 in the Articulata (excepting only the highly aberrant Marsupites), 

 the arm bases occupy only a small part, as in the stalked young 

 of the comatulids. 



7. There are no infrabasals. 



8. There are no pinnules on the arm bases; proximal pinnules 

 are, except in a few very exceptional instances among the coma- 

 tulids, always present in the Articulata; but they are absent in the 

 young of the comatulids until a considerable size is attained. 



9. Tho the pinnules have essentially the same basal structure as 

 those of the Articulata, they are in all ways more generalized, and 

 suggest in many ways ramules or degenerate arm branches rather 

 than perfect pinnules of the Articulata type ; in this they resemble 

 the pinnules of the very young comatulids, or of the growing tip 

 of the arm in larger specimens. 



10. The apex of the dorsal cup shows a tendency to form a con- 

 cavity for the reception of the column. 



11. The column lacks all trace of the modified columnal known 

 as the proximale, but adds new segments at its summit thruout 

 life; in this respect the column resembles that of the young coma- 



