ON THE BRITISH FOSSIL CORALS. 133 



Prof. Agassiz (senior) writes as follows in the ' American Journal of Science 

 and Arts,' 2nd series, vol. xxvi. p. 140, N'ovember 1858 : — 



" The animals of Millepora are Hydroid Acalephs and not polyps ;" that 

 is to say, they are Hydrozoa and not Aetinozoa. The resume of several letters 

 to Dana is given at the same place. ''I have seen," writes Agassiz, "in 

 the Tortugas something very unexpected. Millepora is not an actinoid polyp 

 biit a genuine Hydroid, closely allied to Hydractinia. This seems to carry 

 the whole group of Favositidte over to the Acalephs, and displays a beautiful 

 array of this class from the Silurian to this day." 



Dana adds a note to this statement. " The drawings of Professor Agassiz 

 which have been sent us for examination are so obviously Hydractiuian in 

 most of their characters that no one can question the relation. With re- 

 gard to the reference of all the FavositidtB (a group including Favosiies, 

 Fenestella, PociUopora, &c., as well as the minuter MiUejJora, Chcetetes, &c.) 

 to the Acaleph class, direct evidence is not yet complete, as the animal of the 

 Pocilhpom has not been figured by any author on zoophytes. Prom the 

 specimens of the species of this genus which I procured in the Pacific, I never 

 obtained a clear view of the polyps, and hence made no figure. The brief 

 description on page 523 of my Report may be reasonably doubted until con- 

 firmed by new researches. The much larger cells in Pocillopora, FavosiUs, 

 and Fenestella than in Millepora, and the frequently distinct rays in these 

 cells, are the characters I had mentioned to Prof. Agassiz as suggesting a 

 doubt as to their being Acalephs, and to this what follows above relates." 



Agassiz observes, in a subsequent letter, after observing that the Sidero- 

 porffi obviously are polyps, " There are two types of radiating lamelte which 

 are no£ homologous. In true polyps (excluding Favositidas as Hydroids) the 

 lamella} extend from the outer body-waU inward along the whole height of that 

 wall, and the transverse partitions reach only from one lamella to the other, 

 so that there is no continuity between them, while the radiating lameUte 

 are continuous from top to bottom in each cell. In Milleporidse the partitions 

 are transverse and continuous across the cells ; so are they in Pocillopora and 

 in all Tabulata and Eugosa ; while the radiating lamella?, where they exist, 

 as in Pocillopora and many other Favositida), rise from these horizontal 

 floors, and do not extend through the transverse partitions ; indeed they are 

 limited within the spaces of two successive- floors, or to the ujiper surface of 

 tlie last. A careful comparison of the corallum of Millepora and Pocillopora 

 with that of Hydractinia has satisfied me that these radiating partitions of 

 the Favositida?, far from being productions of the body-wall, are foot-secre- 

 tions, to be compared to the axis of the Gordonia corallum &:c., and their 

 seeming radiating lamellae to the vertical groove or keel upon the surface of 

 the latter, which, reduced to a horizontal ijrojeetion, would also make the 

 impression of radiating lamellas in the foot of the polyp. If this be so, you 

 see at once that apparent radiating lamellae of the Favositidte do no longer 

 indicate an affinity with the true polyps, but simply a peculiar mode of 

 growth of the corallum ; and of these we have already several types, that of 

 Actinoids, that of Alcyonoids, that of Bryozoa, that of Millepora, and other 

 corallines, to which we now add that of Hydroids. Considering the subject 

 in this light, is there any further objection to uniting all the Favositida? with 

 the Hydroids ? Sideropora and Alveopora being of course removed from the 

 Favositida;. It is a point of great importance in a geological point of vicAv, 

 and for years I have been anticipating some such result, as you may sec by 

 comparing my remarks in the ' American Journal,' May 1854, p. 315. If all 

 the Tabulata and Eugosa are Hydroids, as I believe them to be, the class of 



