296 



ECHINODERMATA. 



lacral branchiae upon a rosette formed of large pores on the dorsal 

 surface (fig. 239). The locomotive feet are very small in Clypeastridce, 

 and are distributed either over the whole surface of the ambulacra, 

 or are confined to branching rows upon the ventral surface. In 

 the SpatangidcB there are peculiar bands upon the upper surface, 



the fascioles or semitce (fig. 239), 

 upon which, in place of the spicules, 

 knobbed bristles with active cilia 

 (davulce) are distributed. Develop- 

 ment takes place with a Pluteus larval 

 stage, in which the larva is provided 

 with ciliated epaulettes or with an 

 apical rod. 



The Sea-urchins live, as a rule, 

 near the coast, and feed on molluscs, 

 small marine animals, and Fuci. 

 Some species of HJchinus have the 

 power of boring holes in the rocks 

 in which they live. We find many 

 fossil shells, especially in the chalk. 



FlG. 239. Brissopsis lyrifera with 

 the fascioles or Semites surround- 

 ing the rosette. A, anus. 



Order 1. CIDAEIDEA= REGULAR SEA-URCHINS. 



Echinoidea with central mouth and equal land-like ambulacra; 

 with teeth and masticatory apparatus ; with sub-central anus in the 

 apical space. 



Fam. Cidaridae. With veiy narrow ambulacral and broad interambulacral 

 areas, on both of which are large perforated tubercles and club-shaped spines. 

 There are no oral branchise. Cidaris metularia Lam., Phyllacanthus imperialis 

 Lam., East Indies. 



Fam. Echinidae. Sea-urchins. The pores are grouped in transverse rows ; 

 there is a round, thin shell, broad ambulacral spaces bearing tubercles and spines, 

 which are mostly short and pear-shaped. Oral branchiae are present. Toxop- 

 ncustcs variegatus, Lam., Ecliinus melo Lam., Strong yloccntrotus lividus Brit. 

 saxatilis Lin., Mediterranean. 



Fam. EcMnometridae. With long oval shell, imperforate tubercles and 

 oral branchiae. Ecliinometra oblonga Blainv., Podoplioret atrata Brdt., 

 Acrocladla trlgonaria Ag., Pacific. 



Order 2. CLYPEASTRIDEA. 



Irregular Echinoidea compressed into the form of a shield. Mouth 

 central and furnished with masticatory apparatus. Very broad ambu- 

 lacra, five-leaved ambulacral rosette round the apical pole, and very 



