Gallery 
VIII. 
Table-case 
29. 
Upright 
case A3. 
Table-case 
29. 
Wall-case 
17a. 
70 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
Class OPHIUROIDEA. 
The living Brittle-stars, Sand-stars and Basket-fish are 
separated from tlie star-fishes as a Class, because the arms 
are sharply marked off from the central disc, anti have the 
grooves covered over by plates, and .the flooring-plates of the 
gi’ooves fused into a series of ossicles (little bones) like 
vertebrae, worked on one another by powerful muscles. 
Thus these arms can serve as limbs for locomotion ; and the 
podia, not being needed for that purpose, usually serve oidy 
for respiration and touch. As a further result of this 
development, the arms no longer contain processes from 
the digestive and reproductive systems as they do in 
star-fish. In the Basket-fish the arms may branch, and 
are used for coiling round the stems of other animals or 
plants. 
The Palaeozoic Ophiuroids do not show all these 
points of distinction from Asteroids ; in many of them the 
arm-groove is not completely 
closed, and its flooring-plates 
are not yet fused into vertebrae. 
Species found in the Ordovician 
rocks of Bohemia are still more 
like Asteroids than any here 
exhibited. We begin with British 
Wenlockian forms, such as Lap- 
wortlmra (Fig. 33) and Protaster 
from the Lower Ludlow shales. 
A slightly more advanced type 
is the little Symptcnira from the 
Lower Devonian of Cornwall. 
The Ophiuroids of this age, 
must, however, be studied in the 
Sturtz Collection from Bunden- 
bach, where explanatory labels 
are given. 
Among the British Wenlockian Ojiliiuroidea the most 
remarkable tire Eudadia and its allies ; tor in them the arms 
do not extend beyond the disc, l>ut to make up tor this the 
few podia within the disc limits are of great size, and have a 
flexible armour of small plates. 
From Carboniferous to Trias there are no British 
Ophiuroids, but on the lowest slope ol Wall-case 1/A may 
be seen Onydiaster, from the Carboniterous rocks of Indiana, 
Pig. 33. — A Palaiozoic Ophiuroid, 
Lapiuorthura Miltoni. Lower 
Ludlow shales. Shows the 
mouth-frame in the centre of 
the round body. Between two 
of the rays is the madreporite, 
of which an enlarged figure is 
given. 
