208 ECHINODERMATA ASTEROZOA SUB-BRANCH n 



Sub-Class 2. EUASTERIAE. Bronn. 



Pairs of ambulacral ossicles placed opposite each other, inclined upwards like 

 the rafters of a roof, and united with one another by 'muscles at their inner ends. 

 Madreporite, except in a few Palaeozoic types, restricted to the dorsal surface. 

 Silurian to Recent. 



This sub-class is divided into two orders, depending upon the character of 

 the marginal plates. Both groups make their appearance in the Palaeozoic 

 era, and continue to the present day. 



Order 1. PHANBROZONIA. Sladen. 



Marginal plates large and highly developed ; the supero-marginal and infero- 

 marginal plates contingent. Papulae restricted to the dorsal surface. Ambulacral 

 plates well spaced and usually broad. 



Forms apparently congeneric with the recent members of the Archas- 

 teridae and Astropectinidae are represented in the Devonian. Xenaster, 

 Simonowitsch, a small, five -armed type from the Lower 

 Devonian of Rhineland, has adambulacral and intermediate 

 plates. A large form from the Devonian of Bundenbach, 

 with five long, depressed arms, rectangular adambulacral 

 plates, and two rows of marginal plates, is regarded by Sturtz 

 as 'identical with the recent genus Astropecten, Linck. (Fig. 

 335). Numerous species referred to the same genus have 

 been described from the Lias onwards. 



The genus Luidia, Forbes, has also been considered to be 

 v represented by a form from the Lias. Plumaster, Wright, 



Pentagonaster(T) ^ . J . 



Quenst. from the Lias, is probably a near ally. 



hTm Trichasteropsis, Eck. Central disk large. Arms moderately 



' iSe per e ^ on ' tapering, and covered on the ventral side with spines, 



infero-marginai Marginal plates rather small, except on the dorsal side at the 



plate. C.Plate with f ^ TIT in n 



supposed pedicel- tips of the arms. Muschelkalk. 



St). (after Quen " Pentagonaster, Linck (Goniaster, Ag. p.p.) Body depressed 

 and pentagonal, or with the rays slightly produced. Marginal 

 plates generally few in number, and decreasing in size on approaching the 

 extremity of the ray. Abactinal area covered with rounded or polygonal 

 plates. Cretaceous to Recent. 



Metopaster, Sladen (Goniaster, Ag. p.p.), (Fig. 341). Distinguished from 

 the preceding by the ultimate supero-marginal plates, which are the largest 

 of the series, and by all the marginal plates having a surrounding border of 

 setae. Cretaceous. 



Mitraster, Sladen (Goniaster, Ag. p.p.) Cycloid in contour, with supero- 

 marginal plates few in number, and all of nearly the same size. Cretaceous. 



Calliderma, Gray. Cretaceous to Recent. Nymphaster, Sladen. Cre- 

 taceous to Recent. Pycnaster, Sladen. Upper Cretaceous; England. Lep- 

 taster, de Loriol. Jura. 



Pentaceros, Linck (Oreaster, Mull, and Trosch.), (Fig. 341). Fossil forms 



