92 GEOLOGICAL BIOLOGY. 



6) ; we notice the prismatic form of the corallites, their close 

 crowding together to form a massive colony, like a honey- 

 comb, and the septa are rudimentary, or reduced to mere 

 striae on the inside of the theca, and still further we observe 

 that the theca are perforated by minute holes, and that the 

 tubes are horizontally partitioned off by tabulae, making each 

 to consist of a series of superimposed chambers. These 

 several morphological features are characteristic of the family 

 Favositidae, and we say, therefore, that the family to which 

 the specimen belongs began in the Niagara, and 21 genera 

 are assigned to this family, all restricted to the Paleozoic time. 

 The specimen is also a particular kind of the Favositidae ; the 

 coral is massive, the corallites are closely approximated and 

 sharply polygonal, mostly six-sided, the pores are regular and 

 of definite circular form, the tabulae are regular, of nearly 

 equal distance apart throughout the length of each corallum, 

 and the septa are but rudimentary pseudosepta, and twelve 

 in number. This is a more restricted combination of mor- 

 phological characters and distinguishes the genus Favosites. 

 The genus is limited in range to the Paleozoic, and in the 

 genus there are 53 species found in American rocks. Each 

 of these species has some special mode of growth or size of 

 corallum, or other distinguishing morphological characters, 

 and each species is confined mainly to a single geological 

 epoch, or, at greatest, to a single period ; to the Niagara in 

 the case of F. niagarensis, or to the Hamilton, as F. dumosus, 

 Winchell. 



Geological Eange and Taxonomic Ranks of the Characters. 

 Thus, we may say of Favosites niagarensis, Hall, that its 

 specific characters (speaking only of morphological characters, 

 or the arrangement of matter in a particular mathematical 

 shape) are characteristic of the geological time when the 

 Niagara series of rocks were forming, that is, the lower part 

 of the Silurian system, or the Eosilurian period of time. Its 

 generic characters viz., the massive polygonal tabulate coral- 

 lites, however, have a longer range ; they began in the Silurian 

 and range through the Devonian and Carboniferous eras. 

 Again, its family characters viz., the perforation of the walls, 

 one of the characters of the Favositidae range from a little 



