ECHINO DERMA TA—S Y STEM A TIC RE VIE W 



303 



The old division into Pahvocrinoidea and Kcocrinoidm seems artificial ; that here 

 adopted also cannot be considered as definitive.' 



Order 1. Inadunata. 



Calyx comparatively small ; dorsal cup with monocyclic or dicyelic base ; the 

 basals in the former, and infrabasals in the latter case may be fused to 4, 3, 2, or 

 1. The only other plates in the apical capsule are 5 radials. In the posterior 

 interradius there are very often 1-3 asymmetrically placed anal plates, but no plates 

 in the other interradii. 



The tegmen calycis varies. In some Inadunata (Larviformia) there are 5 large 

 oral plates, which, rising at the edge of the calyx directly above the radials, form a 

 closed pyramid covering the food grooves of the disc, and the mouth. In many 

 other forms the orals (which may be partly resorbed) lie at the centre of the tegmen 

 calycis. The posterior oral plate is often larger than the others, and is shifted for- 

 ward between them. The ambulacra appear at the surface of the tegmen calycis be- 

 tween the oral plates and the edge ; they are bordered on each side by rows of small 

 lateral pieces, the ambulacral groove being also roofed in by small covering pieces.' 

 Plates of various shapes, size, and arrangement are found in the interambulacral 

 regions. In the posterior ambulacral region the tegmen calycis often bulges out in 

 the form of a plated sac, the so-called ventral sac (Fistulata) ; this varies in form 

 and size (sometimes reaching beyond the arms), and may sometimes have contained, 

 besides the rectum, a large part of the body cavity. The anus lies at its tip or on its 

 anterior side. 



Arms free, i.e. not included in the dorsal cup (hence the name Inadunata), 

 simple or branched, with or without pinnulaj. The food grooves of the arms are 

 roofed in by two or more rows of alternating, wedge-shaped, interlocking, ambulacral 

 plates ; these plates could probably be erected. 



Almost exclusively palreozoic forms. 



A. Monocyclica. 



With monocyclic basis (without infrabasals ; several radials often horizontally 



Fig. 247.— Haplocrinus mespiliformis (after Wachsmutli and Springer). A, from tlie anal 

 .side ; B, from the oral side. 1, Orals ; 2, oral pole ; 3, anus ; 4, radials ; 5, right posterior iufer- 

 radial or radianal ; 6, basals ; 7, first brachial ; S, facet for attachment of the arm. 



bisected). Haplocrinus (type of the so-called Larviformia, without anal plate) (Fig. 



' Classification chiefiy after the recent works of Wachsmutli and Springer and Her- 

 Ix-rt Carpenter. See Bibliography, p. 551. 



