330 J. E. Duerden — Jamaican Actiniaria : Part I. — Zoanthece. 



second pair may be composed of two perfect mesenteries (Macrocneminse). In 

 the remaining pairs of mesenteries, of both divisions, this order is reversed, so 

 that the perfect mesentery is sulcar and the imperfect is sulcular. The latter 

 series of mesenteries are bilateral as regards the polyp, and arise independently 

 (i. e. neither in pairs nor symmetrically on each side) in the exoccele on each side 

 of the sulcar directives, in such a manner that the sulcular are the oldest and the 

 sulcar the youngest. Only the perfect mesenteries are fei'tile or bear mesenterial 

 filaments. A single sulcar oesophageal groove is present. The mesogloea of the 

 body -wall is traversed by irregularly branching ectodermal canals or by scattered 

 groups of cells. The body-wall is usually incrusted with foreign particles. The 

 polyps are generally grouped in colonies connected by a coenenchyme, the 

 coelenteron of each polyp communicating with that of the other members of 

 the colony by means of basal endodermal canals. 



Family. ZOANTHID^, Dana, 1846. 



(With the definition of the Group.) 



Sub-family. Brachycnemim:, Hadd. and Shackl., 1891. 



Zoanthese in which the sulcar element of the primitive sulco-lateral pair of 

 mesenteries is imperfect. 



Genera. 



Zoanthus, Lamarck, 1801. 

 Isaurus, Gray, 1828. 



Gemmaria, Duchassaing and Michelotti, 1860. 

 Palythoa, Lainouroux, 1816. 



Sphenopus, Steenstrup, 1856. (Not represented in the West 

 Indian collections.) 



Sub-family. Macrocneminje, Hadd. and Shackl., 1891. 



Zoanthese in which the sulcar element of the primitive sulco-lateral pair of 

 mesenteries is perfect. 



Genera. 



Epizoanthus, Gray, 1867. 



Parazoanthus, Haddon and Shackleton, 1891. 



One of the two type species of the genus Mammillif era, established by Lesueur, 

 having been shown by M c Murrich (1896) to possess all the characters of a 

 Zoanthus, and there being every probability that the other type species, when 

 discovered, will have the same, this genus, formerly included in the Zoanthidaa, 

 can no longer be recognized (see p. 334). 



With the exception of an irregular arrangement of the mesenteries in the 



