108 A Guide to the Zoological Collections in the 



water and toothless forms appear to extract nourishment 

 from the organic matter, animalcules, etc., found in sea-mud. 



The Echinoidea are represented in the exhibited col- 

 lection by the following genera — all from the Indian Seas : 

 — Cidaris, Dorocidaris, Porocidaris, Phyllacanthus, 

 Goniocidaris ; Phormosoma, Asthenosoma ; Diadema^ 

 Echinothrix, Astropyga ; Temnopleurus^ Salmacis, Mes- 

 pilia ; Heterocentrotus, Colobocentrotus, Echinometra, 

 StomopneusteSy Echinostrephus ; Toxopneustes, Trip" 

 neustes, Prionechinus, Fibulariay Clypeaster, Laganum^ 

 Peronella, Echinodiscus, Arachnoides j Echinolampas ; 

 Brissus^ Metalia, Brissopsis, Maretia, Lovenia, Homo^ 

 lampas. 



Besides the above, a small collection of Australian forms 

 is exhibited, and a good collection of fossil types. The 

 fossil specimens are distinguished by a red wafer. 



ECHINODERMA HOLOTHUROIDEA (SEA-CUCUMBERS). 



[©astn-n SeaU-fa0£0 35-36]- 



The Holothuroidea are long worm-like or cucumber- 

 shaped Echinoderms with a thick leathery skin which is 

 usually soft and strengthened, though but slightly, with 

 scattered microscopic spicules and perforated platelets of 

 various form composed of carbonate of lime. In one small 

 group of deep-sea Holothuroidea, however, represented in 

 the collection by the beautiful specimens of Deima, the in- 

 tegument consists of a continuous mosaic of large calcareous 

 plates which form a rigid test not unlike that of a Sea- 

 urchin. In the Holothurians the water-vascular system 

 undergoes a remarkable modification ; it becomes more 

 respiratory and less locomotor in function, the ambu- 

 lacra being reduced in number to three or to two, or even 

 disappearing altogether {Synapta, Caudina), while round 

 the mouth the system becomes extended into a crown of 

 large and often much-branched oral tentacles : these are 

 displayed, fully extended, in the specimen of Thyone in 

 Case 35. 



