REVIEWS 237 
the Larviformia and Fistulata. The former has the disk in its simplest 
possible form, being made up of five large orals arranged in a pyramid ; 
the second has the ventral side extended into a sac or closed tube, often 
reaching beyond the ends of the arms. 
The Camerata are distinguished by the large number of supple- 
mentary pieces which bring the proximal arm plates into the calyx, 
thus enlarging the visceral cavity. All plates are heavy and immov- 
able andthe mouth and food grooves are tightly closed. 
The Articulata have to some extent the incorporation of the lower 
arm plates with the calyx, but the plates are movable instead of rigid. 
The mouth and food grooves are open. The infrabasals are fused 
with the top stem joint which is not the youngest plate of the stalk. 
According to whether or not the pinnules are present two suborders 
are recognized: the Pinnata and Impinnata. 
For the family distinctions the supplementary plates constitute 
excellent features for classification, and while of small importance 
physiologically, they form a good example of a truth which is met 
with everywhere in biology that characters of physiological value are 
not always of equally great utility for purposes of classification. Of 
prime import in this regard are the anal pieces. 
Of the three groups of crinoids having ordinal rank, that constitut- 
ing the Cameratais by far the most important. An analysis of the 
families is briefly as follows: 
I. Lower BRACHIALS AND INTERBRACHIALS FORMING AN IMPORTANT PART OF 
THE DORSAL CUP. 
A, Interradials poorly defined. 
Lower plates of rays more or less completely separated from those of 
other rays and from primary interradials by irregular supplementary 
pieces; anal interradius divided by a row of conspicuous plates; 
(dicyclicxonmmonocyclic))yaryaecrecte iss aloe aniins cine etser ra ae RETEOCRINIDA 
B. Interradials well defined. 
1. Dicyclic. 
a. Radials in contact, except at the posterior side..... THYSANOCRINID& 
i, INechens seer! alll eheorbGl ano 6isooad accaaoooasenKe RHODOCRINID-E 
2. Monocyclic. 
a. Radials in contact all around. Symmetry of the dorsal cup if 
not strictly pentamerous, disturbed by the introduction of anals 
Daniean Ie ACU OMY, so>5000000 09000000 bs 00000005 MELOCRINIDA 
Arms borne in compartments formed by partitions attached to 
tegmen; dorsal cup perfectly pentamerous; plates of calyx lim- 
ited cOnardehnite mumberuces serie sc oriacmcicre ee moeee CALYPTOCRINID 
