136 J. E. DuERDEN — Jamaican Actiniaria : 



only a single tentacle communicates with a mesenterial chamber) and Stichodacty- 

 linse (in which more than one tentacle may communicate with a mesenterial 

 chamber), has the advantage of being founded upon an external character which 

 can be readily observed, and which must certainly be regarded as of some funda- 

 mental importance in Actinian morphology. 



For better comparison of the tentacular relationships, I give a plan of a 

 portion of the disc in each case. 



It is doubtful as to how far the Stichodactylinous condition is homologous 

 throughout the order, for important differences obtain in each of the seven species 

 to be described. 



In the Phymanthidse the marginal tentacles are in numerous, alternating, 

 entacmseous cycles, arranged exactly as are the tentacles in the Actiniufe. The 

 inner, so-called tentacles are nothing more than mere discal tubercles, more or 

 less irregularly arranged, and histologically differ entirely from the outer 

 series. From the evidence afforded by its peripheral tentacles, I regard the 

 family as approaching the Actininae more closely than any of the others. 



The arrangement is somewhat similar in Actinotryx, but the marginal 

 tentacles are all in a single cycle, though they probably represent two or three 

 series for some reason not separated centripetally. The disc tentacles are 

 irregularly arranged with regard to the mesenterial chambers ; and their dendritic 

 form is perhaps but an exaggeration of the tubercular tentacle of Phymanthus. 

 The arrangement of the outer and inner groups in Actinotryx recalls that in 

 Corallimorphus, though the form of the tentacles presents a great contrast. 



The case of Corynactis is otherwise. So far as my experience goes, no 

 distinction can be made between a peripheral and an inner series, though Haddon 

 (1898, p. 466) makes a generic character of such a separation. The tentacles in 

 each radial series follow one another in regular sequence, and afiord the same 

 histological details, pointing to a common origin ; the relative sizes are, however, 

 the reverse of those in the Actininse, i.e. the inner are the smaller, and the outer 

 the larger. 



A somewhat similar arrangement holds in the genera Stoichactis and Ricordea. 

 The tentacles in the same radial row follow one another in a regular manner ; but 

 with regard to the conditions at the margin, however, the species vary. In 

 Stoichactis heliantlms a single outermost cycle alternates with all the radial rows. 

 In Ricordea florida^ on the other hand, the outermost cycle but one alternates with 

 all the rows within, and with the cycle peripheral to it ; these two marginal cycles 

 are somewhat larger, and are often of a colour distinct from that of the inner 

 tentacles. 



Homostichanthus possesses about a dozen outer cycles of tentacles, often 

 distinguished from the inner series by the innermost cycle being differently 



