MORPHOLOGICAL PART. 59 
h and 2, respectively, are united (Fig 13). As this structure is apparently 
constant in the latter group, we regard it as of some importance as regards 
classification. 
The introduction of the anal plate did not affect the basals of dicyclic 
Crinoids in the same manner as in the monocyclic. While in the latter, 
when the plate is represented, the orientation of the basals is slightly dis- 
turbed, in the dicyclic forms it remains unaltered. The anal plate of the 
latter rests invariably upon the truncated upper face of the posterior basal 
(see Figs. 14 to 18); while in monocyclic Crinoids it is supported by the 
basals a and e (Figs. 10 and 12), or occasionally by a and zx (Fig. 8). 
The infrabasals are completely anchylosed in the Cupressocrinide, Gas- 
terocomide, and in Stemmatocrinus, where they form an undivided disk, which 
Carpenter and others have regarded as representing the top stem joint, as in 
the case of the Apiocrinide and Comatule. Ayassizocrinus, in its pedun- 
culate younger state, had five well defined infrabasals; but after losing its 
stem, the suture lines became gradually obliterated by limestone deposit 
upon the surface. The same is the case with the basals of the monocyclic 
Edriocrinus. 
Mr. Bather discriminates between Dicyclica, Pseudomonocyclica, and 
Monocyclica vera.* To the Pseudomonocyeclica he refers those forms in 
which infrabasals are obsolete in the adult, but were represented in early life. 
They embrace most of the Mesozoic and recent Crinoids, and may be sub- 
divided into two classes: (1) forms in which the infrabasals gradually 
become anchylosed with the top stem joint, and (2) those in which they 
were resorbed in the adult. In the former, which among other groups 
include the Apiocrinidze and Comatule, the new stem joints are formed below 
the centro-dorsal ; while in the latter, which are typified by the Pentacri- 
nide, the top stem joint is the youngest joint of the stem. We shall 
presently show that both these forms, although the infrabasals may have 
disappeared, still retain the characteristics of dicyclic Crinoids. 
Several years ago we discovered t that among the Paleocrinoidea there 
is a regular alternation in the arrangement of the successive parts below the 
radials, and that the orientation of the stem is essentially different among 
monocyclic and dicyclic forms. We found that the salient angles of the stem 
itself, and the projections of the axial canal, are reversed in the two eroups, 
* Ann. and Mag. of Nat. Hist. (sixth series), Vol. V., April, 1890, p. 316. 
f Revision, Part III, Section I, p. 7 (Proceed. Phila. Acad., 1885, p. 229), with a most unfortunate 
transposition of terms, which was corrected in the appendix. Also 1888, Proceed. Phila. Acad. p, 351. 
