DISTRIBUTION IN TIME. 173 



but indications of a minute foramen, quite insufficient for the transmission of a comparatively thick 

 tentacle like that of any known hyJroiii. 



On the whole, though ihe autliors liave clone good service to Palaeontology by making us 

 acquainted with this remarkable little tenant of Carboniferous seas, I cannot accept their views 

 of its affinities, and I believe that we must seek for these with the Ithizopoda rather than with 

 the IIydroiua. 



Fossils, exclusive of Ihc graptuHlcs, which have been correctly referred to hijdroid irnphosomes. 

 — Of the hydroid nature, however, of certain other fossils which have been detected in various 

 geological formations there can be no doubt. Instances are known of the chitinous basis of 

 Ilj/dracliiiia having been preserved in a fossil state. Under the name of Cellepora echinata ]M. 

 Michelin has described a fossil from the sub-apennine group of Asti, and from the superior 

 Fallunian of Bordeaux and Dax.^ M. Fischer has drawn attention to the fact that the 

 Cellepora echinata of i\lichelin is really a llydractinia encrusting a Murex or a Nassa, while he 

 has himself added another fossil Hydraclinia from the Upper Greensand of Mans.^ This he 

 found in the collection of jM. Ale. d'Orbigny, where it encrusted numerous specimens of Natica 

 tuberculafa, d'Orbig., from that formation. M. Fischer has assigned to this species the name of 

 llydraciinia cretacea, while to Micheliu's species he has given that of Hi/dractinia Michelini. 



To the two examples thus noticed by Michelin and Fischer I am enabled to add a third 

 from the Coralline Crag of Norfolk and Suffolk. It occurs among some Coralline Crag fossils in 

 the collection of the British Musemn, where it encrusts two specimens of Purpura lapillus, one 

 from Orford, in Norfolk, and the otiier from Redgrave, in Suffolk. It covers with a continuous 

 crust the shell over which it spreads, and has a minutely alveolar structure, w'ith its surface 

 thickly set with short blunt spines. The original chitine is entirely replaced by carbonate of 

 lime. There cannot be the slightest doubt of its being a true Hi/dractinia, and, indeed, it is 

 impossible to find any characters which can separate ^it from the living Hydractinia echinata. 

 From the mere fossilised basis, however, which is, of course, all that has come down to us, we 

 should not be justified in absolutely asserting its identity with the living hydroid. 



M. Fischer gives no specific description of the specimens to which he assigns two dis- 

 tinguishing names, and it is probable that no characters of diagnostic value can be detected 

 sufficient to distinguish them from one another or from the Coralline Crag specimens, or even 

 from our living Hydractinia echinata. It is by far most likely that such characters would be found 

 if an opportunity existed of examining in the fossils the soft parts now entirely lost, more 

 especially when we bear in mind that they lived at such distant intervals of time as those which 

 separated from one another the cretaceous, meiocene, pleiocene, and existing epochs. 



If, under these circumstances, we should be justified in assigning to the Coralline Crag 

 species a distinguishing name when no available characters can be found on which a diagnosis 

 can be based, this may be derived from its geological position, and the purely provisional 

 designation of Hydractinia pleiocena may be given to it. 



Among fossil hydroids Serfularella polyzonaas, one of the most abundant and most widely 

 distributed species of the present seas, has been cited from the later Pleistocene deposits of 

 Ayrshire.' 



^ jMiclieliu, ' Icou. Zoopli.,' p. 7^>, pi. xv, fig. 4. 



" Fischer, ' Bull, de la Soc. Geol. de France,' 2 ser., tome xxiv, p. 689. 



' ^Morris, ' Caliil. Brit. Fossils,' p. 63. 



