110 PROCEEDINGS OF THE ACADEMY OF [1889. 



organs that such a proceeding was considered unnecessary. It seems 

 probable that the genus Lophactis should be fused with Oulactis. 



DIPLACTIS. Gen. nov. 



I propose this generic name for two species, one of which is des- 

 cribed below, which do not seem to be referable to any of the genera 

 now recognized. The genus maybe briefly defined as follows: — 

 Phyllactidse in which the fronds are represented by a single cycle of 

 short digitiform tentacles and in which all the mesenteries except 

 those of the first cycle are gonophoric. The term Diplactis has 

 been chosen as indicating the tentacular appearance of the fronds, 

 from which it seems as if there were two series of tentacles, an inner 

 and an outer (diplous, double and aktis, a ray). 



In the Supplementary Report on the Actiniaria collected by the 

 " Challenger," R. Hertwig describes a form whose locality is un- 

 known, which he refers to Gosse's genus Hormathia. It is very similar 

 to the form about to be described from the Bermudas, and there can 

 be no doubt that though specifically distinct the two must be referred 

 to the same genus. Gosse's Hormathia 1 was described from a single 

 specimen brought up on a deep-sea fishing line, and attached to the 

 shell of a living Fusils. It was characterized by possessing slightly 

 below the margin about ten spherical protrusions. I do not think 

 it is possible to associate in the same genus with this either the Ber- 

 muda Diplactis or Hertwig's Hormathia. In the first place in both 

 these forms the bodies near the margin are digitiform and not spheri- 

 cal ; and secondly, these bodies are situated not below the margin but 

 internal to it. In all the Bermuda specimens, of which there are 

 quite a large number, a well-marked margin is present and Hertwig 

 describes in his form a fold of the column-wall which must be con- 

 sidered equivalent to the margin of the other species. Although the 

 margin cannot be considered of importance as marking the bound- 

 ary of the disc, yet it is a structure of frequent occurrence and must 

 be taken account of. Structures that occur on the column-wall be- 

 low it, as in Hormathia, cannot be considered identical for systematic 

 purposes with others which invariably lie above or internal to it, and 

 are not quite similar in form. 



It must be noticed that Haddon has recently referred to Gosse's 

 Hormathia a form 2 altogether different from that assigned to it by 



1 P. H. Gosse. Actinologia Britannica. London. IStJO. 



2 A. C. Haddon. — On two species of Act'nise from the Mer^ui Archipelago. — 

 Journ. Linn. Soc. Vol. XXI. 1888. 



