INTRODUCTION. 41 



adambulacralia and the inai-g'inalia ; and the sio-nificance of the fact tliat certain 

 forms are characterised l)y alternating" rather than l)y oj)posite ambnlacralia also 

 appears to have escaped notice. 



An advance was made by Bronn (1860, 14, pp. 217 — 218), who divided the 

 extinct genera into three divisions : 



(1) T]ie Encrinasteriae. Asteroids with alternating ambnlacralia and a ventral 



madreporite. 



(2) The Euasteriae. Asteroids with opposite ambnlacralia and a dorsal 



madreporite. 

 {'■]) The Ophiurasteriae (the Ophiuroidea). 



It is important to take notice of this classification as the terms have been much 

 nsed by later systematists. 



The Second Period. 



The second period includes the work of Stiirtz, published in 1886 [76), 

 1890 (78), 1893 (79), and 1899 (80), and the Avork of Gregory, 1896 (26), 1899 

 (27), and 1900 (28). 



Stiirtz described a number of forms from the Bundenbach (Devonian) Slates 

 of Germany. The original calcite and frequently even the integument was, at 

 some period, pyritised, and the forms can be developed by metallic brushes, which 

 clear away the matrix more readily than the specimen. The great majority of the 

 originals were afterwards purchased by the British Museum (Natural History), 

 and were examined and compared with English specimens by Gregory. 



(a) TIte Classification of the Ojjliiuroidea. — Stiirtz regarded a number of the 

 Palaeozoic forms as true Ophiuroidea. As a basis for the classification of these 

 Ophiuroidea the sub-division proposed by Johannes Miiller was adopted. 



Sub-order 1. The Ophiurse (Sandstars and Brittle-stars). 



Forms with undivided arms, dorsal and ventral shields and usually mouth- 

 shields. 

 This sub-order contains three groups of Recent forms. 

 Group Ophioijltjphidse. 

 „ AiiipJduridce. 

 „ Opliioniijxidse (or A>it ropli ijton-Y\\e Ophiurans). 



Sub-order 2, Euryalae (Medusaheads, Astrophytidse of Lyman). 



Forms with dichotomously branching arms usually covered with a skin con- 

 taining small calcifications. Dorsal, ventral, and mouth-shields absent. 



6 



