148 J. E. DuERDEN — Jamaican Actiniaria : 



covering nearly the whole of the disc, while there is a marked difference, both in 

 form and histology, between the marginal and discal tentacles in Actinotryx. 



In important anatomical details, such as the deep stomodseal folds, absence of 

 gonidial grooves,- and ciliated streak, Actinotryx and Ricordea are related; but, 

 excepting perhaps the last mentioned, evidently not much reliance can yet be 

 placed upon these for indicating broader relationships. 



It is a question of choosing between external characters, and internal anatomy 

 and histology as the chief factors of relationship. In the order Stichodactylinse, 

 at any rate, I am of opinion that the best results will be attained by giving the 

 greater prominence to the arrangement of the tentacles among the former. The 

 frequent multi-oral condition of the disc occurring in both, must assuredly be 

 looked upon as a specific peculiarity. 



Haddon (1898, p. 477) includes the four genera, Rhodactis, Actinotryx, 

 Ricordea, and Heterantlius in the family. The second genus was instituted by 

 Duchassaing and Michelotti (1860, p. 45) for a West Indian form, which later was 

 regarded by M^Murrich as allied to the Rhodactis rhodostoma of the Red Sea, and 

 was therefore transferred to that genus. From details of this species sui^plied 

 by Dr. Carlgren, Haddon (p. 477) considers that the two should remain as 

 distinct genera, and this is the conclusion I have followed. 



Genus.— ACTINOTRYX, Duchassaing & Michelotti. 



Actinotrtjx, . . Duchassaing and Michelotti, 18G0 ; Andres (Actinothrix), 



1883 (pars); Haddon, 1898. 

 Rhodactis, . . M'Murrich, 1889. 



Rhodactid^, in which the column is smooth. Marginal tentacles short, in two 

 or three series, but forming only one cycle ; inner tentacles dendritic or lobed, 

 2)artly separated into a middle discal group and a perioral group. Sphincter 

 muscle feeble or absent. An ectodermal muscular layer on the column-wall and 

 stomodseum. Stomodaeum deeply furrowed. No gonidial grooves. Mesenterial 

 filaments devoid of ciliated streak. 



The history of the genus has just been given under the discussion on the 

 family. 



Actinotryx Sancti-Thomae, Duch. & Mich. 



(PI. X., figs. 3-6; PI. XL, figs. 3, 4; PL xii., fig. 3). 



Actinotrijx Sancti-Thomte, Duchassaing & Michelotti, 1860, p. 45, pi. vii., 



fig. 2 ; 1866, p. 35. 

 Actinothrix Sancti-Thomcc, Andres, 1883, p. 509. 

 Rhodactis Sancti-Thomce, M'^Murrich, 1889, p. 42, pi. i., fig. 9, pi. iv., figs. 2, 3. 



