POLYZOAN CORALS 



165 



by the presence of the large orifice for the protrusion of the 

 Polyzoan polyp. 



Retepora. — One of the commonest objects in a museum 

 collection of Polyzoa is the beautiful little coral frequently 

 called " Neptune's basket " (Manchette de Neptune, Tour- 

 nef) (Fig. ^^). 



Its most characteristic form is that of a shallow bowl, 

 from one to two or three inches in diameter, attached by 

 a short round stalk to a shell or stone. The bowl is per- 

 forated throughout by numerous round holes or fenestra 

 about 075 mm. in diameter, situated at regular intervals 

 apart so that it has 

 the appearance of a net 

 or basket, and was in 

 consequence given the 

 name Retepora by Im- 

 perato in 1599. Later 

 observers, noticing 

 that the upper surface 

 of the coral exhibited 

 a large number of 

 minute pores, classified 

 it with many other 

 corals under the general 

 name Millepora, and 

 thus it became the Millepora cellulosa of Linnaeus. 



The genus Retepora has a wide geographical distribu- 

 tion, being commonly found in the temperate seas, in the 

 Mediterranean, and in the Tropics. There are two British 

 species, both found in deep water : R. heaniana occurring 

 off the coast of Northumberland and Scotland, R. couchii 

 in the Channel Islands and off the coast of Cornwall. 



The colour of the coral is usually white, but in some 

 localities (Torres Straits, Bass Straits, etc.) pink or salmon- 

 coloured specimens are not uncommonly found. The bowl 

 shape of the colony, which is by far the most characteristic 

 form, is in some specimens replaced by a more irregular 

 manner of growth leading up to forms that may be called 

 foliaceous ; but in these varieties the characteristic features 



I'"iG. 77. — Retepora. Nat. size. 



