MORPHOLOGICAL PART. 87 
erius, in which they completely envelop the calyx, exposing their ventral 
surfaces. 
The mobility of the arms in the Camerata must have been limited, as we 
nowhere find at the apposed faces of the various brachials any trace of a 
muscular attachment. Those brachials which take part in the calyx are, 
like the other calyx plates, united with one another and with adjoining 
plates by close suture, the apposed surfaces being flat and generally smooth, 
rarely striated ; and the plates are immovable. The first indication of any 
kind of articular facet occurs on the highest plate of the calyx; 7. e., that 
bearing the free arms. This plate is usually more or less concave, often 
striated, sometimes having a sort of ball-and-socket arrangement, or being 
provided with an obscure transverse ridge; and in a few cases it is perfo- 
rated. The faces of the higher arm plates are smooth or striated, and but 
little concave; yet there must have been a considerable amount of mobility 
even among them, for the tips of the arms are frequently curved inward, and 
in some cases the arms are decidedly spreading. 
The mode of union between the brachials of the earlier Fistulata was 
similar to that of the Platycrinide. The Dendrocrinide and Cyathocrinid 
have more or less well developed facets upon the radials, and the arm 
plates are united among themselves and with the radials by ligaments 
only, so as to admit but little motion. In the later Fistulata, however, 
notably the Poteriocrinide * and Encrinide, there is a muscular articula- 
tion between the axillaries and the joint succeeding them, as in recent 
Crinoids. 
The Larviformia, so far as they are known, have a well differentiated 
muscular articulation, with transverse ridge and fossee between the radials 
and costals, but not between the succeeding brachials. Cupressocrinus, Allage- 
erinus, and Symbathocrinus have large muscle plates connected with the radi- 
als; while the other brachials are so closely united one to another that it 
appears as if the whole arm had moved rigidly upon the radials. 
In the Ichthyocrinide all the brachials, whether fixed or free, are mov- 
able. The calyx was pliable from the radials up, as is shown by the apposed 
faces of the plates, which are deeply hollowed out; not only those of the 
brachials, but the interbrachial plates as well. The cavities, which evi- 
dently lodged large bundles of ligament, contain small elevations with stri- 
* It is unfortunate that the genus Poferiocrinus has been made the type of this family. It is the only 
genus of the Poteriocrinide in which the facet supporting the arms is horse-shoe-shaped, and the eostals do 
not occupy the full width of the radials, which is so characteristic of the family. 
