124 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
although the mouth in most of them remained closed throughout life, was 
not morphologically distinct from that of the Crinoids of existing forms, and 
that the so-called “vault” has been developed gradually from the disk. 
The Camerata, therefore, cannot be the progenitors of recent Crinoids ; they 
represent a side group, which in the course of Paleozoic time departed 
essentially from the primitive type, reaching the culmination of extravagance 
in form and size in the Carboniferous, and becoming extinct at the close 
of that epoch, 
B. The Anal Plates and the Anus. 
The Anal plates bear a most important part in the phylogeny of Palzxo- 
zoic Crinoids, and are also of high importance in respect to classification. 
Some writers apply the term “anal plates” indiscriminately to all interradial 
plates of the posterior area, while others restrict it to the plates directly or 
indirectly connected with the anus. We apply the term to the latter plates, 
but only to such of them as take part in the dorsal cup; the others being 
plates of the anal tube or ventral sac. 
The anal plates in all Camerata, when present, occupy the median line of 
the posterior area, so as to divide the interbrachial plates into two equal 
sets; and in rows containing an odd number they have the effect, as it were, 
of breaking up the middle plate into two, even in cases where no anal plate 
is inserted between the segments. The latter is the case in the Actino- 
crinide, in which the first interbrachial row at the posterior side always 
consists of two plates, in place of one as in each of the others; though all 
have an anal plate between the radials, and an extra plate in the second 
interbrachial row. In the Batocrinide and Thysanocrinidx there are two 
interbrachial pieces above the first anal, which enclose a second anal piece. 
The Hexacrinidz have but one large anal plate resting upon the basals. 
The Eucalyptocrinide have no anal plate at all, the five interbrachial areas 
being perfectly symmetrical. Such is the case also in Dolatocrinus, Stereo- 
crinus, Centrocrinus, Allocrinus, and Patelliocrinus ; while the typical Melo- 
crinidee have an anal plate in one or more of the upper rows. Similar 
variations occur among the Rhodocrinids, in which anal plates may be 
either present or absent. The -Platycrinide have no special anal piece, but 
the middle plate of the proximal row at the posterior side is considerably 
enlarged, and evidently united the functions of an anal plate with those of 
the regular interradial. 
