Hjdractinia, Parkeria, and Stromatopora. 5'J 



Ohs. By comparing the description of the skeleton ot" lly- 

 dractinia echinata with that of H. pliocena^ it will at once be 

 seen that I must differ from Dr. Allman where he states {I. c.) 

 that " it is impossible to find any character which can sepa- 

 rate it [H. pliocenci\ from the living Hydracthiia echinata^ 

 Here Dr. Allman assumes that the original composition of 

 H. pUocena was chitinous, and that this has been " entirely 

 replaced by carbonate of lime." But now that the living 

 Cape-Palmas specimen shows that the skeleton of Hydractinia 

 may be calcareous as well as chitinous, it seems to me much 

 more probable, as the skeleton of the calcareous species is 

 solid and shows no signs of fibre, that H. pUocena, which also 

 shows no signs of fibre, was also calcareous. 



Of the identity of the large and small spines of H. pliocena 

 with those of the living species there can be no doubt. Nor 

 can we doubt that the apertares on the surface leading down 

 to the chambers (which, although present in H. echinata, are 

 not so plainly marked as in H. calcarea) are equally identical 

 with those on the surface of H. pliocena. Of the identity of 

 the grooved reticulation on the surface of H. echinata, where 

 the coenosarcal branched stolon-tubulation which produces it 

 is also present, with the branched grooved reticulation on the 

 surface of H. pliocena (fig. 8, h h) there can also be no doubt ; 

 while the annular constriction in the descending tubes of the 

 latter is equally identical Avith the annulation of the pedicels 

 on the coenosarcal tubulation oi H. echinata, together with the 

 diaphragmatic rings which are seen at the bottom of the tubes, 

 more es2)ecially in H. calcarea. 



The presence of some of the small spines on the floors of 

 the chambers (fig. 9, e d) is the same, and the hollow radial 

 form of the internal cavity of the large spine closed at the 

 summit the same as that of the large spine also especially seen 

 in H. calcarea (fig. 6, a,h). 



So that altogether, part for part, we have just the same 

 formation in H. pliocena as in the living species, while the 

 structure of the fossil is more like that of H. calcarea. 



Lastly the large spines in H. pliocena are for the most part 

 broken off by accident, and thus present a hollow interior ; 

 but where perfect the summit will be found to be closed or 

 imperforate. 



Hydractinia Vicaryi, n. sp. (PL VIII. fig. 11.) 



Skeleton thick, incrusting. Composition siliceous. Colour 

 greyish white. Surface rough, uniformly granulated with 

 small obtuse spines interrupted by larger ones, over which the 



