MORPHOLOGICAL PART. 87 



crinus, 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 ; i. 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 earher Fistulata was 

 similar to that of the Platycrinidae. The Dendrocrinidae and Cyathocrinidse 

 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 Poteriocrinidae * and Encrinidae, 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 fossae between the radials 

 and costals, but not between the succeeding brachials. Cupressocrinus, Allage- 

 crimis, and Si/mhathocrimis 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 Ichthyocrinidas 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, w^hich 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 Toteriocrinus has been made the type of this family. It is the only 

 genus of the Poteriocrinidae in which the facet supporting the arms is horse-shoe-shaped, and the costals do 

 not occupy the full width of the radials, which is so characteristic of the family. 



