90 GEOLOGICAL BIOLOGY. 



genera, or classes, or subkingdoms ; but we see only certain 

 shells, or impressions, or marks on the rocks : we say these 

 fossils represent animals that have lived, and we give them 

 particular generic and specific names. To take an example, 

 we find a specimen in the Niagara limestone, illustrated in 

 the accompanying figure. (Fig. 6.) 



The Fossil Coral, Favosites niagarensis, as an Illustration. It 

 was named Favosites niagarensis by Hall, which means that 

 its generic characters are those of the genus Favosites, its 

 specific characters those of the species F. niagarensis, and 

 that it was described by the paleontologist James Hall. It is 

 a fossil coral (Actinozoan), of the order Zoantharia. 



Analysis of the elements of form, which must be observed 

 in classifying the specimen, will reveal somewhat more dis- 

 tinctly what is meant by saying that organic form and lapse 

 of time are intimately associated. We notice, in the first 

 place, that the fossil is made up of a large number of polygo- 

 nal calcareous tubes attached together by their outer faces. 

 This peculiar structure is the evidence for placing it in the 

 order Zoantharia. Living corals (Zoantharia) secrete calcare- 

 ous tubular bases, in and upon which each Zooid is supported, 

 and in living corals these corallites are aggregated in the same 

 manner as in the specimen before us. The radially sym- 

 metrical structure of the corallites is sufficient evidence that 

 the specimen belongs to the subkingdom Coelenterata, and 

 we know of the existence of this subkingdom in the first or 

 Cambrian period. 



The continuous, hard, calcareous skeleton shows the fossil 

 to be a Madreporarian, the structure of whose soft parts we 

 assume to have been that of living Madreporarians, and there- 

 fore to be one of the class Anthozoa which is characterized as 

 "polyps with oesophageal tube and mesenteric folds, with in- 

 ternal generative organs (no medusoid sexual generation)." 

 The septa, which are rudimentary in the species before us 

 (see Fig. 8), are twelve, and this character distinguishes the 

 specimen from the subclass Tetracoralla, in which the septa 

 are grouped in multiples of 4, and from the order Alcyonaria, 

 which has 8 tentacles; and they show it to be an Hexactinia 

 (or Hexacoralla), in which the septa are six or some multiple 



