CLASS III 



CRINOIDEA 185 



may be present, even when the special anal is wanting ; they arc interposed between the 

 interbrachials, following the median line of the posterior area. 



Orals = T\ie five large interradial plates which surround the mouth or cover it. They are 

 said to be symmctriccd when of nearly the same size and form ; asymmetrical when the 

 posterior plate is pushed in between, or is larger than, the other four. 



Ambi(,lac7-als = The rows of small plates in the tegmen which are radially situated. They 

 consist of adamhulacrals or side-pieces, and the covering -iilates (Sauvipldttehen). The former, 

 when present, constitute the outer, the latter the inner rows of plates. The covering i)lates 

 form a roof over the food-grooves ; they are generally represented by two alternating rows 

 of small plates, more or less regular in their arrangement, which are movable upon the arms 

 and jnnnules, but upon the disk only in those Crinoids in which the mouth is exposed. 



The orientation is based upon the natural position of the Crinoid, with the arms upper- 

 most, and viewing the specimen from the anal side. The anal interradius will then be 

 posterior, the radius opposite to it anterior, while the right and left sides of it correspond 

 with right and left of the observer. 



Primary Divisions of the Crinoidea. 

 I. 



Crinoids in which the lower brachials take part more or less in the dorsal cup. 

 All plates of the calyx united by close suture. Mouth and food-grooves closed. — 

 Order 1. Came rata. 



II. 



Crinoids in which the lower luachials are incorporated into the calyx either by 

 lateral union with each other, or by means of a skin studded with calcareous particles. 

 All plates from the radials up movable. Mouth aird food-grooves exposed. Arms 

 non-pinnulate. The top stem joint often fused with the infraljasals, and not always 

 the youngest joint of the stem. — Order 2. Flexibilia of Zittel { = Articulata of W. 

 and Sp. non Miller and Miiller). 



III. 



Crinoids in wliich the brachials are free above the radials. Plates of calyx united 

 by close suture. Mouth sub-tegminal. — Order 3. Inadunata. 



IV. 



Crinoids in which the mode of union of radials with the plates they liear is by 

 complete muscular articulation, and in which are combined the following additional 

 characters : open mouth and food grooves ; dorsal canals perforating radial and arm 

 plates ; uniserial arms only ; pinnules ; the general presence of a modified columnal, 

 or proximale ; the general absence of bilateral, and presence of pentamerous symmetry, 

 modified only by loss or addition of rays and not by anal structures. Brachials either 

 free, or more or less incorporated. — Order 4. Articulata. 



The first three of these divisions are represented in the Ordovician. The Camerata 

 were the most specialised, and the first to disappear, being confined to the Paleozoic, 

 and becoming extinct in the Lower Coal Measures. The Flexibilia were similarly 

 limited. The Artic^data range from the Mesozoic to the present time. The Inadunate 

 type, representing the most generalised structure of the Crinoids, is in its most 

 essential feature, though variously modified, carried forward with the Articulata, and 

 thus has an unbroken range from the earliest Ordovician to the present. 



Order 1. CAMERATA Wachsmuth and Springer. 



{Sphaeroiclocrinacea Neumay r. ) 



Crinoidea in which the lower brachials take part in the dorsal cup. All plates of 

 the calyx united by close sutures, and immovable. Mouth and food-grooves completely 



