22 



PROP. P. MAETiN" Duncan's eeyiston or the 



otlierg which have endured from the Cretaceous age to the pre- 

 sent day, and some which flourished during the Eocene and still 

 exist. Some genera are dwellers in tlie deep sea. Any turbi- 

 nate-shaped species of the genus TrocTiocyathus and any form of 

 the genus Ceratotrochus may be taken as the types of the two 

 great groups of the alliance, the one with and the other without 

 pali. 



Genus Teochocyathtjs, MM. Milne-Edwards Sf Jules Haime, 

 Ann. des Sci. Nat. 3^ ser. t. ix. p. 300 (1848), amended. 



Syn. AplocyatJius, d'Orb. ; Stephanocyathus, Seguenza ; Flaty- 

 cyatJius, E. de Erom. 



The corallum is simple, pedunculate or subpedicellate, or 

 merely shows the trace of a former adhesion. The shape may be 

 elongate, turbinate, subturbinate, straight, curved, compressed 

 or not, or more or less discoid and flat. The calice is deep or 

 widely open. The septa are long and usually some are exsert. The 

 pali are in two crowns. The columella is formed of trabeculse, 

 is essential, and may or may not be papillary. The costss may 

 or may not be well developed, crested, spined, or simply projecting. 

 Epitheca variable. 



Distribution. — Fossil. Lias to Eecent. Fossil forms world- 

 wide. — Becent. "West Indies, South- Australian seas. 



The genus is a large one, and should include some subgenera. 

 Its species have been divided into the following groups by 

 Milne-Edwards and Jules Haime : — Trocliocyatlii striati, with 

 the wall marked with but slightly projecting costse ; and Trocho- 

 cyatJii armigeri, with the costse well developed, crested, spined, 

 or warty. In both of these divisions the shape of the coral is 

 very variable. 



Subgenus Tropidoctathtts, Ed. Sf H. 



The corallum is compressed ; the wall is naked, and has a basal 

 expansion. Pali before all the cycles except the last, and they 

 form more or less marked chevrons. 



Subgenus TnECOCYATHrs, Fd. Sf H. 



The epitheca surrounds the wall and reaches the calicula 

 margin. Corallum with a fixed and broad base, or not fixed. 



