186 A. E. Verrill — Comparisons of Coral Faunce. 



On the other hand, Favia: leptophylla Ver. closely resembles an 

 Orhicella, and especially the Brazilian Orbicella aperta Ver., not only 

 in external form and appearance, but especially in the internal struc- 

 ture, both of the endotheca and exotheca (see the figured sections. 

 Plates xiii and xxxiii, from photographs). Indeed, they are so much 

 alike that I have, at times, hesitated to keep them apart, even as sep- 

 arate species. 



And yet the former increases mainly by median or submedian fis- 

 sion, as in Favia, while the latter increases mainly by extramural or 

 exothecal budding, as in typical Orhicella. In O. aperta, however, 

 fission occasionally occurs, while a few exothecal buds can be found 

 on Favia leptophylla. 



Thus these two forms serve to show the close relationship of two 

 genera, which are typical of two groups, often considered as of 

 subfamily or even family rank. I very much regret that I have 

 been unable to study a large series of these forms, for such a series 

 might even compel us to unite the two in one species, which might 

 then be referred to either genus, about equally well. 



Siderastrma stellata is, in several ways, intermediate between 

 8. radians and S. siderea, the two West Indian species, though per- 

 haps nearer to the former. It may well have been the ancestral 

 form of both. 



Meandrina [Fectinia) Braziliensis must be considered as a primi- 

 tive or ancestral form of its genus, for it retains through life the sim- 

 ple lobulated condition of growth characteristic of the young of the 

 much larger and more complex forms (M. tneandrites, etc.) found in 

 the West Indies, 



The Brazilian Agaricia, so far as known, resembles the young of 

 the West Indian A. agaricites much more than the adult. 



Very few of the Brazilian reef corals are strictly identical with 

 those of the West Indies. This is due, undoubtedly, to the vast vol- 

 ume of fresh Avater discharged by the Amazon River. This forms a 

 barrier absolutely impassable to many forms of shallow-water marine 

 animals, and to their free-swimming larval stages, when these live at 

 the surface or at moderate depths. Those species living at the bot- 

 tom, at considerable depths, would be less affected, for the fresh 

 water would reach the bottom only at moderate depths, and near 

 the coast. 



But as the reef corals are all sensitive to brackish water, and all 

 inhabit shallow water and have free-swimming, surface-dwelling 

 larvse, they naturally form one of the groups least able to pass such 



