192 FOSSIL ACTINOZOA. 



excluded from the Astrceidce. In the Columnarice proper 

 ( - Favistella) the septa are very well developed, but in 

 other forms often referred here (fig. 77) the septa are 

 rudimentary. 



Leaving the Palaeozoic period, we find a great develop- 

 ment of Astrceidoe to take place towards the close of the 

 Trias where the family is represented by numerous and varied 

 types ; a still further expansion takes place in the Oolites ; 

 very numerous forms are met with in the Cretaceous, and 

 though there is some decrease in the Tertiaries, this great 

 family still holds its ground as the most important group of 

 the " reef-building " corals. 



Of the many genera of this family, only two or three of 

 the most important can be so much as alluded to here. Of 

 the simple forms of the family, we may 

 take Montlivaltia (fig. 78), and Trochos- 

 milia as typical examples the former 

 genus ranging, under many specific forms, 

 from the Triassic to the Tertiary inclu- 

 sive ; while the latter, also with many 

 species, begins in the Jurassic, and con- 

 tinues to the later Tertiaries. These 

 simple types may be regarded as transi- 

 tional between the Astrceidce and Tur- 

 *olidce. Such forms as Thecosmilia (fig. 

 covering the "79^ again, may be compared to a colony 



" 



lower part of the coral. ,,- , 7 . 7 , ,1 -IT, 



Great Oolite. ot MonUivaUice, the separate corallites 



being bound together by a strong "epi- 

 theca," and united into a tufted corallum. The species 

 of the genus are numerous, and are found in the Juras- 

 sic, Cretaceous, and Tertiary periods. In a third group 

 of Astrceidce we have very numerous and important forms, 

 which agree with the last mentioned in being compound, but 

 in which the corallum consists of numerous closely-approxi- 

 mated corallites, produced by fission, and giving rise, as a 

 rule, to massive " astrseiform " colonies. Of these " star- 

 corals," Astrcea itself may be taken as the type, though not 

 known to have existed earlier than the Tertiary. In the 

 Secondary period, however, we have a vast development of 



