CHARACTERISTIC DEEP-SEA TYPES. CORALS. 



149 



Two species of the genus Thecocyathus have been dredged, 

 and are not uncommon in from 100 to 315 

 fathoms. One of these, T. cylindraceus, is 

 here figured. (Fig. 464.) The genus is inter- 

 esting as dating back to the lias ; it is not 

 known from any of the formations inter- 

 mediate between the lias and our epoch. 

 The recent forms present, therefore, a com- 

 paratively rare instance of the reappearance 

 of a genus apparently extinct through a con- 

 siderable succession of ages. 



Deltocyathus italicus (Figs. 465, 465 u-d) is an exceedingly 



Fig. 4C.5 a . 



Fig. 465. 



Fig. 405 d. 



Deltocyathus italicus. |. (Pourtales.) 



Fig. 465 6. 



variable living form of a tertiary fossil common in Sicily. The 

 polyp of a large living specimen, dredged in 115 fathoms off 

 the Tortugas, was whitish, with short club - shaped tentacles. 

 A most variable species is Paracyathus confertus. (Fig. 466.) 

 Stephanotrochus diadema (Fig. 467) seems to be a character- 

 istic deep-sea type. It has been dredged in 734 fathoms off 



