234 Miscellaneous. 



lopora, &c, as well as the minuter Millepora, Chcetetes, &c.) to the 

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

 the Pocillopora has not been figured by any author on Zoophytes*. 

 On this point Professor Agassiz states in a subsequent letter, after 

 observing that the Sideroporce obviously are polyps : — 



" There are two types of radiating lamellae, which are not homo- 

 logous. In true Polyps (excluding Favositidae as Hydroids) the 

 lamellae extend from the outer body-wall 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 lamellae are continuous from top to bottom in 

 each cell. In Milleporidae the partitions are transverse and con- 

 tinuous across the cells, and so are they in Pocillopora and in all 

 Tabulata and Rugosa ; while the radiating lamellae, where they exist, 

 as in Pocillopora and many other Favositidae, rise from these hori- 

 zontal floors, and do not extend through the transverse partitions ; 

 indeed they are limited within the spaces of two successive floors, or 

 to the upper surface of the last. A careful comparison of the coral- 

 lum of Millepora and Pocillopora with that of Hydractinia has 

 satisfied me that these radiating partitions of the Favositidae, far 

 from being productions of the body-wall, are foot-secretions, to be 

 compared to the axis of the Gorgonia, Corallium, &c, and their 

 seeming radiating lamellae to the vertical grooves or keels upon the 

 surface of the latter, which, reduced to a horizontal projection, would 

 also make the impression of radiating lamellae in the foot of the 

 polyp. If this be so, you see at once that the apparent radiating 

 lamellae of the Favositidae 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 

 Halcyonoids, that of Bryozoa, that of Millepora and other Corallines, 

 to which we now add that of the Hydroids. Considering the sub- 

 ject in this light, is there any further objection to uniting all the 

 Favositidae with the Hydroids, — Sideropora and Alveopora being of 

 course removed from the Favositidae ? It is of great importance 

 in a geological point of view, and for years I have been antici- 

 pating some such result, as you may see by comparing my remarks 

 in the 'American Journal,' May 1854, p. 315. If all the Tabulata 

 and Rugosa are Hydroids, as I believe them to be, the class of Aca- 

 lephs is no longer an exception to the simultaneous appearance of all 

 the types of Radiata in the lowest fossiliferous formations, and the 

 peculiar characters which these old Hydroid corals present appear in 

 a new and very instructive aspect." — Sillimari s Journal, July 1858. 



* From 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 rea- 

 sonably doubted until confirmed by new researches. The much larger size 

 of the cells in Pocillopora, Favosites, and Favistella 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 Aca- 

 lephs, and to this what follows above relates. — J. D. D. 



