130 PROCEEDINGS OF THE NATIONAL MUSEUM. 



Science the PMladelphia Academy of Sciences, the private cabinet of 

 Mr. Joseph Willcox, of Philadelphia, and the Johns Hopkins University. 

 The state of preservation of the forms is as a rule excellent, with the 

 exception of the silicified corals from Florida. These latter are often 

 very difficult of determination, owing to prefossil wear and the minera- 

 loo-ical change the specimens have since undergone. Frequently the 

 poorly preserved calices alone remain, the entire inside of the individ- 

 ual or the colony being dissolved away and represented by a cavity 

 with walls of botryoidal character. W hen the original substance of the 

 coral with the exception of the outer surface, is thus replaced, it becomes 

 impossible, as an aid to identification, to cut sections showing the coral 

 structure below the calice. The cause and method of silification of 

 these corals has never been satisfactorily proven. Professor Heilprin,i 

 in discussing the phenomena in his treatise on the Explorations on 

 the West Coast of Florida, attributes the change to an infiltration of 

 silica in a heated condition, but adds that he can not even hazard a 

 guess, much less explain in what precise manner the peculiar method 

 of hollowing was brought about. Especially is this true of the colonial 

 types with botryoidal- shaped cavities. Furthermore, in the genera 

 possessed of very small calices, as in Porites and Stylopliora, their deli- 

 cate structure is often so destroyed as to render a specific diagnosis 

 impossible. 



The writer has also been at a great disadvantage from the fact that 

 a number of the species have been described from single specimens, 

 and until further collecting is done in the field it will be impossible to 

 give a more detailed specific description of these forms. 



The fauna under discussion embraces in its geological distribution, 

 the Neocene and Oligocene epochs. On the other hand, geographically 

 the range of these forms is remarkably confined. With the single excep- 

 tion of a few casts from the Miocene of Griswoldville, Fresno County, 

 California, we find them limited to the Atlantic seaboard States, from 

 New Jersey to Florida, inclusive. 



In considering this fauna as a unit, its most striking feature' is the 

 great number and variety of the genera represented as compared with 

 the species, there being twenty-eight of the former to thirty-five of 

 the latter. This proportion of genera to species is quite unusual, the 

 number of species in any given fauna more often being far in excess 

 of the genera. As an instance, we may cite the present fauna of 

 Bermuda, with its twenty-eight species to only ten genera, or the 

 results reported by the Challenger, which during its entire cruise 

 obtained only sixty-nine genera of reef corals to two hundred and 

 niuety-three species, and many of these presenting considerable varia- 

 ation. We find, further, in taking account of the Neocene corals, that 

 the colonial far outnumbers the individual type. 



In examining the bathymetric distribution of the species, it is doubt- 



1 Trans. Wagner Free Inst. Sci., I, p. 62. 



