J. E. Duerden — Jamaican Actiniaria : Part I. — Zoanthece. 345 



Gonads (PI. xvm. a, fig. 4). — Ova and spermaria are borne in close proximity 

 on the perfect mesenteries, both above and below the oesophagus. They were 

 met with in three specimens taken from the same colony, but none were present in 

 several examples sectionized from another colony. 



Coenenchyme. — The ccenenchyme is of similar structure to the body-wall, but 

 the mesoglcea is much thicker and broken up by large ciliated ccelenteric canals 

 passing in all directions; the endodermal lining is loaded with zooxanthellse, and 

 has a weak musculature. Isolated cells with fine processes, and the smaller 

 ectodermal canals occur. 



For some time during the preparation of this Paper, I had regarded this 

 species, with little or no hesitation, as the Mammillifera nymphcea of Lesueur 

 (1817). In the meantime, Prof. M c Munich identified, with some amount 

 of uncertainty, a form from the Bahamas as Lesueur's species. The external 

 characters of the Jamaican representative agree with those of the Bahaman, as 

 far as the latter are given, but a comparison of the sphincter muscles shows that 

 they are undoubtedly distinct. Prof. M c Munich, from an examination of my 

 material and slides, entirely agrees with this. Whether his identification of the 

 Bahaman form with that which Lesueur described be correct or not, it seems 

 best that his conclusion should he followed for the future, seeing that with the 

 addition of the anatomical features, the characters of the species are definitely 

 fixed once for all. There must nearly always be an amount of uncertainty in 

 identifying the species of the older authors, where external characters only were 

 taken into account. I have therefore changed my manuscript identification of 

 this species to that of Mammillifera pule hella of Duchassaing and Michelotti (1866), 

 a form these authors regarded as a doubtful variety of M. nymphcea. 



Isaurus, Gray, 1828. 



Large brachyenemic Zoanthese, with a single mesogloeal sphincter muscle. 

 The body-wall is unincrusted ; the ectoderm discontinuous ; ectodermal and 

 endodermal bays and small canals in the mesoglcea. Monoecious or dioecious. 

 Polyps in small clusters or solitary. 



Prof. Haddon and Miss Shackleton give (1891, pp. 682-4) a full discussion of" 

 the genus defined by them as above. They dwell particularly upon the reason 

 why it should not be merged into the genus Mammillifera of Lesueur, as / 

 accepting the characters Erdmann gives (1888, p. 35), has been done by 

 M c Munich (1889, p. 117). In his more recent paper (1896, p. 191), the latter 

 author adopts Isaurus. 



THANS. EOV. DUBI. SOC, U.S. VOL. VI., PART XIV. 3 Gr 



