400 COELENTERATA ANTHOZOA CHAP. 



authorities are not agreed as to its limits or classification. 

 Excluding the simple forms for the present, the family may 

 be said to be distinguished by having the calices so closely 

 crowded that there is little or no coenosteum between them. 

 The corallum is compact and massive, unless bored and perforated 

 by algae, worms, and other coral-destroying organisms. 



The genera of Astraeidae that form colonies may be divided 

 into two groups : the Gemmantes and the Pissipaeantes. In 

 the group Gemmantes asexual reproduction is effected by gemma- 

 tion, and each zooid of a colony is a distinct individual with two 

 pairs of directive mesenteries. Among the best known of recent 

 corals included in this group may be mentioned Galaxea. In 

 this genus there is a good deal more coenosteum between the 

 calices than there is in most of the Astraeidae. The calices are 

 long and project some distance above the coenosteum. The 

 septa are exsert. In Galaxea esperi examined by Fowler^ there 

 are twelve septa, twelve pairs of mesenteries, and twenty-four 

 tentacles, of which twelve are very small and twelve rather 

 larger. The colour is green or brown. The genus is found in 

 shallow water in the tropics of the old world. 



In Astrangia solitaria the zooids are either isolated or more 

 generally united by thin strands of perithecal tissue to form 

 encrusting colonies. The septa are not exsert as in Galaxea. 

 Six are prominent and belong to the first cycle, six smaller ones 

 form a second cycle, and an incomplete third and fourth cycle 

 may be seen. Corresponding with each septum there is a 

 tentacle. The tentacles of the innermost cycle are the longest 

 (3 mm. in length). All the tentacles terminate in a knobbed 

 apex. The living zooids are colourless throughout, or display 

 only very delicate tints within restricted areas.^ This genus 

 occurs principally on the coasts of the American continent, 

 extending as far south as the Straits of Ma.gellan. Other 

 well-known genera of Astraeidae Gemmantes are Orhicella, 

 Cladocora, Phyllangia. 



In the group Fissipaeantes asexual production takes place 

 by fission without the production of morphologically complete 

 zooids. The tentacles, mesenteries, and septa, when fission is 

 established, are not arranged in regular hexameral cycles, and no 



1 G. H. Fowler, Quart. Journ. Micr. Sci. xxx. 1890, p. 410. 

 " J. E. Duerdon, Mem. Ac. Washington, viii. 1902, p. 553. 



