498 CLARK: CRINOID FAMILY PLICATOCRINIDAE 



columns of the pentacrinites and of the Bourgueticrinidae it may 

 be mentioned that the earhest nodals in the young pentacrinite 

 column resemble far more the syzygially united columns in the 

 bourgueticrinoid column than they do the nodals of the adult, 

 for they are much elongated, and the cirri are usually defective, 

 three, two, or sometimes only one, in number. 



It is evident that the structure of the Plicatocrinidae in all of its 

 details corresponds very closely to that of the young comatulids 

 before the appearance of the columnal which is eventually to form 

 the centrodorsal ; it is also evident that this family can scarcely 

 find a logical position among the Articulata, from all of the other 

 forms in which it differs so radically. 



The order Inadunata of Wachsmuth and Springer includes Cri- 

 noidea in which the arms are free above the radials; the dorsal 

 cup is limited to radials, basals, infrabasals (when present) and 

 anal plates; no interradials nor interbrachials occur except at the 

 posterior (anal) side, and the brachials are never incorporated 

 in the cup; all the plates of the cup are united by close suture; the 

 mouth is subtegminal ; the column is circular in section (with very 

 rare exceptions), without a proximale. 



It is at once evident that the Plicatocrinidae agree with the mem- 

 bers of this order far better than they do with those of the Articu- 

 lata, differing only in a lack of a distinct differentiation of the 

 posterior area, and in the possession of open food grooves and an 

 open mouth. But in the Encrinidae, which are referred to this 

 order, the posterior area is in no way different from the others, 

 while in at least three of the recent genera of the Plicatocrinidae 

 it is not quite the same, so that this difference is very slight. In 

 many of the fossil Inadunata we do not know the disk; while 

 among recent types the genera of the Plicatocrinidae have the 

 deepest food grooves and the nearest approach to a subtegminal 

 mouth; it may be that in reality this apparent difference is non- 

 existent. 



A rapid survey of the various families of the Inadunata — in 

 the suborder Larviformia the Stephanocrinidae, Pisocrinidae, Hap- 

 locrinidae, Allegecrinidae, Synbathocrinidae and Cupressocrinidae, 

 and in the suborder Fistulata the Hybocrinidae, Heterocrinidae, 



