134 ECHIXODERMATA PELMATOZOA SUB-KINGDOM in 



The Radiuiidl (= first or lower anal plate auct. ), when present, rests within the re-entrant 

 angle of two adjoining basals to the right of the true anal plate, and is the lower half of a 

 bisected radial, which only in certain genera assumes anal functions. 



Orats = Ti}ie five large interradial plates which surround the mouth or cover it. They are 

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

 plate is pushed in between the four others. 



Ambulacrals = r l\z rows of small plates in the tegmen which are radially situated. They 

 consist of adambidacrals or side-pieces, and the covering-plates (SaumplattcJien). The former, 

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

 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 

 pinnules, 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 uppermost, 

 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 correspond with right and left of 

 the observer. 



Primary Divisions of the Crinoidea, according to W. and Sp. 



I. 



Crinoids in which the arms are free above the radials. The topmost joint the 

 youngest in the stem. Order 1. INADUNATA. 



(a) Disk composed of orals only. Ambulacra subtegminal. Sub-Order A. Larviformia. 



(b) Posterior side of the disk extended into a sac. Ambulacra supra tegminal. Sub-Order 



B. Fistulata. 



II. 



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

 the calyx united by close sutures. Mouth and food-grooves closed. The top joint 

 the youngest in the stem. Order 2. CAMERATA. 



III. 



Crinoids in which the lower brachials 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 and food-grooves exposed. The top 

 stem joint fused with the infrabasals, and not the youngest joint of the stem. -Order 3. 

 ARTICULATA. 



(a) Arms non-pinnulate. Sub-Order A. Impinnata. 



(b) Arms pinnulate. Sub-Order B. Pinnata.] 



Order 1. LARVIFORMIA. Wachsmuth and Springer. 



(Haplocrinacea, Neumayr.) 



Tegmen formed by five triangular orals only, arranged in the form of a pyramid. 

 Dorsal cup composed of basals and radials exclusively, except in the Cupressocrinidae, 

 where the basals enclose a central undivided plate. All plates immovably united by 

 close sutures ; arms feebly developed. Ordovician to Carboniferous. 



Mostly small forms exhibiting embryonic characters persistently throughout 

 life. 



Family 1. Haplocrinidae. Roemer. 



Calyx small, pyriform to globose. Three of the radials compound, the others simple. 

 Orals large, triangular to pentagonal, laterally in contact. Arms jive, uniserial, non- 

 pinnulate. Devonian. 



