'o 



XIII. Odontocyathus Moseley. 



Odontocyathus Moseley, Challenger Deep Sea Madreporaria p. 14.S. 



There are ihree dead and broken specimens in the collection which are referable to this 

 genus rather than to Stephanotrochus. 



Synopsis of the Siboga species of Odontocyathus. 



I. Corallum ;i bowl standing on legs formed by the six primary costa;: 



i. Septa strongly exsert, edge of bowl deeply scallopped i. O. sexradiis. 



2. Septa little exsert, edge of bowl not scalloped 2. Odontocyathus sp. 



II. Corallum perfectly flat, converted into a star by the six large horizontal 



septa and costaa of the first cycle 3-0. stellet. 



26. Odontocyathus sexradiis n. sp. Plate III. Fig. 20, 20a — 6. 



Stat. 156. o°2q'.2S., i30°5'.3E. 469 m. 1 Ex. 



The corallum is bowl-shaped, with the edges very deeply scallopped between the enor- 

 mously exsert primary septa, and is supported on six long, strong, solid, smooth, radiating 

 legs, which correspond in situation with the primary septa. 



The costs are but little more than ridges markeel only on the sides of the bowl, not 

 on the base where there is a smooth mammillar scar. 



The septa are in six systems and five cycles, with a sixth cycle developed in some of 

 the quarter-systems. Those of the first cycle are the largest and and far the most exsert, and 

 they carry up with them those of the inferior cycles lying immediately on either side of them, 

 which therefore are more exsert than all the other septa of the same and higher cycles below 

 the first. The septa of the fourth cycle unite with those of the thircl some way before the 

 latter reach the columella. 



Pali are present, in three crowns, opposite the first three cycles of septa, and in those 

 half-systems in which a sixth cycle of septa is partially developed there are also pali opposite 

 the fourth cycle. The pali of the innermost crown are the smallest, and those of the outermost 

 crown are the largest. 



There is an abundant fasciculate or radiculate columella, with which the first three 

 cycles of septa unite. 



Major diameter of calicle 43 millim. 



Minor , „ „ 34 



Greatest height, to summit of the exsert primary septa 28 „ 

 Least height, in interval between two primary septa .18 „ 



Length of rootlets over 20 „ 



This species is evidently very closely related to Stephanotrochus Tatei Dennant, from 

 the South Australian Tertiaries (Trans. Roy. Soc. S. Australia XXIII. 1898 — 99, p. 117, 

 PI. III. Figs. ia—c). 



