II\ ilinctiiiia, Paiki-ria, and Slnjinatupoia. 5.'J 



(fhs. Wy (•i)iiij)ariiii^ tli(; description i>t' tli(^ skeleton ol ////- 

 dnirtinut tcltiiKitti with that of //. /dinrcna^ it will at once bo 

 seen that I must ditler from Dr. Allnian where he states {Lc.) 

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

 rate it [//. jdiocnui] from the livint:: Jli/dractinin crhinatay 

 Here Dr. Allman assumes that the original composition of 

 //, idiorena was ehitinous, and that this has been " entirely 

 replaced by carbonate of linu'." liut now that the living 

 (Jape-I*alinas specimen shows that the skeleton o'l Ilijdracliniti 

 nuiy be calcareous as well as ehitinous, it seems to me much 

 more prol)able, as the skeleton of the calcareous species is 

 solid and shows no signs of fibre, that //. pliorcna, which also 

 shows no sigTis of fibre, was also calcareous. 



( )f the identity of the large and small spines of //. ph'ocena 

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

 can we doubt that the apertures on the surface leading down 

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

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

 with those on the surface of //. i^Uocena. Of the identity of 

 the grooved reticulation on the surface of //. echinata^ where 

 the ca'uosarcal branched stolon-tubulation which produces it 

 is also j)resent, with the branched grooved reticulation on the 

 sui'facc of //, jdfocena (fig. 8, h h) there can also be no doubt ; 

 while the annular constriction in the descending tubes of the 

 latter is equally identical with the annulation of the pedicels 

 on the coenosarcal tubulation of//, echinata., together with the 

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

 more especially in H. calcarea. 



The presence of some of the small spines on the fioors 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. G, «7, Z'). 



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

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

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



Lastly the large spines in //. pUocena 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. (PI. VIII. fig. 11.) 



Skeleton thick, incnisting. Composition siliceous. Colour 

 greyish white. Surface rough, uniforndy granulated with 

 snuill obtuse spines interrupted by larger ones, over which the 



