HyJractiuia, Parkcriaj and Stromatopora. 51 



and fig. 6, «), communicating at the base with the interval 

 between the two laminaj, closed at the summit (fig. 4, f) ; 

 massive, but radiate in structure, the ends of the radii corre- 

 sponding to serrulated ridges on the surface of the spine 

 (fig. 6), which ridges diminish in number upwards until by 

 union they form the summit of the cone (fig. 6, h). Small 

 circular ajDertures, about l-600th inch in diameter, plentifully 

 scattered among the serrulated points of the rugged ridges and 

 bases of the large spines (fig. 5, ccc), which are the openings 

 of short tubular cavities, that respectively end in diaphragms 

 with a small circular hole where they open into the interval 

 between the two lamina3 (fig. 4, g g). Diaphragms about 

 5-1 sooths inch in diameter, apparently continuous with 

 the chitinous membrane lining the internal cavities, and, for 

 the most part, visible through the apertures on the surface. 



Hah. Marine, incrusting small univalve shells. 



Loc. Cape Palmas, Guinea coast, Africa. 



Ohs. There are two specimens of this species, viz. one on a 

 small 3fu7-ex about eight twelfths of an inch long, bearing two 

 spines equally covered by the Jig dr actinia, and the other on 

 a broken shell of the same size and kind. Each shell contains 

 a hermit crab (Pagurus). They were sent to me in a dry 

 state ; and failing to obtain, by soaking in warm water, any 

 return of form in the soft parts beyond that of thread-cells, I 

 am unable to describe more than the skeleton. With the 

 exception of the skeleton being massive and not reticular and 

 chitinous, it is otherwise so like that of Hydractinia echmataj 

 that, on a superficial view, it would, but for the colour, be 

 said to be the same species. 



Fossil Hydractiniid^. 



We now come to the fossil species of Hydractiniida?, viz. 

 //. Michelini and H. cretacea, Fischer — the former from the 

 Upper Miocene and Older Pliocene respectively, and the latter 

 from the Upper Greensand (Bull, de la Soc. Geol. de Fr. 

 t. xxiv. p. 689, 1857) ; also H. pUocena^ Allman, from the 

 Older Pliocene or Coralline crag of Suffolk ; to which I can 

 add another species from the Upper Greensand of Haldon Hill, 

 near Exeter, lent to me by my kind friend Mr. W. Vicary, of 

 Exeter, after whom I shall call it H. Vicaryi. 



Deferring M. Fischer's species for the present, we shall 

 commence with H.j)Uocena) and as Dr. Allman has not entered 

 into a sufficiently detailed description of this species for our 

 present purpose, I shall describe it from the specimen to which 

 I have before alluded, which has grown over the outside of a 



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