296 



ECHIKODERMATA. 



lacral branchise 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 Spatamjidfe there are peculiar bands upon the upper surface, 



the fascicles or semitce (fig. 239), 

 upon which, in place of the spicules, 

 knobbed bristles with active cilia 

 (clavulce) 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 Echinus have the 

 power of boring holes in the rocks 

 in which they live. We find many 

 fossil shells, especially in the chalk. 



FIG. 239. Brissopsi* lynfera with 

 the fascicles or Semites surround- 

 ing the rosette. A, anus. 



Order 1. CIDABIDEA= REGULAR SEA-URCHINS. 



Echinoidea with central mouth and equal band-like ambulacra ; 

 ivith teeth and masticator)/ apparatus ; with sub-central anus in the 

 apical space. 



Fam. Cidaridae. With very narrow ambulacra! and broad iaterambulacral 

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

 There are no oral branchise. Cidaris metiilaria Lam., Plu/ll acanthus 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 branchirc are present. To.wjt- 

 ni'//xf<'x i-itrh'i/utiix. Lam., Echinus mdo Lam., Strong ylocentrotus Hri/fun Brit. 

 saxatllis Lin., Mediterranean. 



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

 oral branchia?. Ki-liiinniirira oblong a Blainv., PodopJiora atruta Brdt., 

 Acrocladla trlyonaria 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 



