ECHINODERMATA—ASTEROZOA SUB-BRANCH II 
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. PHANEROZONIA. 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 Stiirtz 
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 

Fia. 339. 
Pentagonaster (?) 
impressue,  Quenst. 
sp. Upper Jura; 
Reichenbach im 
Thale. A, Supero- 
marginal plate. B, 
Infero-marginal 
plate. C, Plate with 
supposed _ pedicel- 
lariae (after Quen- 
stedt). 
represented by a form from the Lias. Plumaster, Wright, 
from the Lias, is probably a near ally. 
Trichasteropsis, Eck. Central disk large. Arms moderately 
long, tapering, and covered on the ventral side with spines. 
Marginal plates rather small, except on the dorsal side at the 
tips of the arms. Muschelkalk. 
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. 34). 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.) Cyeloid 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, Mill. and Trosch.), (Fig. 341). Fossil forms 
