200 BRITISH PALEOZOIC ASTEROZOA. 



a lateral view of one of the arms towards the extremity shows that there was 

 a covering of small plates. 



The structure of the oral interradial area, inasmuch as only the odontophor 

 and proximal infero-marginalia are present, suggests in a generalised way the 

 structure of a TJrasterella (compare Text-fig. 8G, p. 134). In fact, Schuchert 

 (1915, p. 186), from the very slender account of the species given by me in the 

 Introductory Section to this Monograph, imagined that it might belong to a 



Text-fig. 147. — Drawing (somewhat diagrammatic) of Eoactis simplex (reproduced from Plate I, fig. I). 

 A lt first ambulacral ; Ad ly first adambulacral ; F u cup for first tube foot ; MA. P., mouth-angle plate. 



TJrasterella. I do not know any TJrasterella which shows such a very definitely 

 differentiated first pair of infero-marginalia, and there is no evidence of the 

 " TJrasterelln paxilla." I regard its generalised features as being those common to 

 very many primitive Asterozoa, and consider that we can most pertinently regard 

 it as illustrating the structure of the basic member of a series which gave rise to 

 Schuchertia, Palasterina and Pakvosolast<"r, each of which tends to depart more and 

 more from the " primitive Asterozoan " appearance as a specialised mode of life is 

 acquired. 



1. Eoactis simplex, Spencer. Plate I, fig. 4; Plate XV, fig. 8; Text-figs. 



147, 148. 



1914. Eoactis simplex, Spencer, Brit. Palaeoz. Asterozoa (Mou. Pal. Soc, vol. for 1913), p. 30, pi. i. 



fig. 4. 



1915. ? TJrasterella girvanensis, Schuchert, Bull. 88, U.S. Nat. Mus., pp. 173, 178, 186. 

 1915. Eoactis simplex, Bather, Geol. Mag. [6], vol. ii, p. 320. 



Material. — One impression in the British Museum (Nat. Hist.), no. E. 13154, 

 originally no. G57 of the G. H. Morton Collection. The oral surface only is 

 shown. 



Specific Characters. — As those for genus. 



Description. — Text-fig. 147, which is reproduced from PI. I, fig. 4, of this 

 Monograph, illustrates most of these characters. The groove is open and shows 



