100 A Guide to the Zoological Collections in the 



Goniodiscus; Pentaceros, Culcita^ As'terodiscus ; Anthenea; 

 Asterina ; Linckiay Ophidiaster, Nardoa^ ChxtasteVy 

 Fromia ; Echinaster, Acanthaster ; Asterias. 



(2) From the deep-sea : — Pararchaster, Pontaster^ 

 Dy taster y Persephonaster^Pseudarchaster ; Porcellanaster, 

 Styracaster, Hyphalaster; Dipsacaster; Petitagonaster, 

 Calliaster, Milteliphaster, Nymphaster^ Paragonaster^ 

 Mediaster, Anthenoides ; Palmipes ; Zoroaster ; Hymen- 

 aster, Marsipaster ; Pedicellaster ; Brisinga, Freyella. 



2. ECHINODERMATA OPHIUROIDEA. (BRITTLE 

 STAR-FISHES). 



[©astern Mnll-cnQts 24-26.] 



The Ophiuroidea resemble the Asteroidea in external 

 form ; but the arms, which very rarely exceed five in 

 number, are relatively much longer and more attenu- 

 ated, and are much more clearly and sharply marked off 

 from the disk ; and the disk is more circular and relatively 

 of much smaller size. In the Asteroidea, again, as is seen 

 in the dissections in Cases ig and 21, the stomachal caeca 

 pass into the arms, as do also the generative organs ; but in 

 the Ophiuroidea^ as is seen in the dissections in Case 25, 

 the viscera are entirely confined to the disk and do not 

 extend into the arms. In the Ophiuroidea also an anus is 

 always wanting. 



On examining a typical Ophiurold, such as the large 

 specimens of Ophiothrix galatese in Case 26, we see that 

 the animal consists of a small round disk, in which the 

 viscera are lodged, and of five long thin snaky arms orrays. 



The disk, on the upper surface, is seen to be covered 

 with small scales the surface of which is beset with little 

 spinelets, while the arms are enclosed in much larger 

 scales or plates, of which those at the sides bear long 

 flat spines in several series. Five pairs of plates at the 

 margin of the disk, near the bases of the arms, are much 

 enlarged : these are known as the " radial shields." 



On the under surface of the disk we see, in the centre, 

 the mouth bounded by five pairs of mouth-plates (one of 



