230 REVIEWS 
in the Fistulata rest upon the edges of large interradial pieces. When 
the ambulacra are subtegminal they enter the calyx by the arm open- 
ings, and follow the inner floor to the proximity of the mouth. 
The ‘supplementary plates” comprise all calcareous particles 
between the basals and orals, and between the rays and their subdivis- 
ions. ‘They are interradial, interaxillary or anal. The interradial plates 
which are separated into interbrachials and interambulacrals, comprise 
all pieces between the basals and orals interradially disposed, the for- 
mer being confined to the dorsal cup ; the interambulacrals occupy only 
the spaces between the ambulacra. The interaxillaries, which consist 
of the interdistichals and interpalmers are located within the axils of 
the second and third orders of brachials respectively. The anal plates 
are restricted to the posterior interradial area, and support the anal 
tube. Another system of supplementary plates occurs in the acro- 
crinidz, between the basals and radials. In groups in which the arms 
are not entirely free from above the radials, the lower arm plates are 
incorporated into the calyx by means of interbrachials; and the orals 
are carried inward toward the actinal center by interambulacrals. The 
supplementary plates increase in number in the growing crinoid. 
They are undeveloped in the early larva and in the Laviformie. In 
the Fistulata they are represented only in the tegmen, except in the case 
of the anal piece. The plates vary exceedingly in form and character, 
being in some groups well developed and rigid, in others irregular 
and imperfectly formed or mere lime particles within soft tissues. The 
great variation in the structure of the plates formerly led to the belief 
that the rigid and regularly arranged pieces, so characteristic of the 
Camerata, did not belong to the same system as the irregular small 
pieces which unite the rays inrecent form. A distinction was also made 
between the ossicles of the tegmen. ‘The heavy, rigid components of 
the paleozoic forms called “vault” pieces the irregular smaller ones 
“‘disk”’ plates ; and it was supposed that many of the older crinoids 
had a vault with adisk underneath. ‘That they had two integuments 
was believed to be indicated by the condition of the ambulacra, which 
in recent crinoids are exposed, while in paleeozoic types they are either 
completely subtegminal, or the food grooves are rigidly closed by 
immovable covering pieces. This supposition, however, has proved to 
be an illusion and to be based upon inaccurate observation. Even in 
species of Batocrinus and Dorycrinus, in which deception seemed to be 
almost impossible, it is ascertained from excellent material, that the 
