lOO 



5. TROCHOCYATHUS RAWSONII (Pourtales) (PI. i, fig. 

 2, a, b, and PI. II., figs. A-K). 



■ . rawsonii, Pourtales, Cat. Mus. Comp. Zool, Harvard, 

 Vol. IV., p. 35, pi. VI., figs. 7-IO (1871), and Bull. Mus. 

 Comp. ZooL, Harvard, Vol. V., p. 199 (1878). 



I refer no less than 38 dried specimens to this species, though 

 their general type differs from the description of the species in 

 the fact that the shape is conical, with base varying in breadth 

 up to one-third the diameter of the calicle. This, however, is 

 probably purely a matter of environment, and Nos. 31 and 32 

 of the table are in this character typical members of T. raw- 

 sonii. 



The species characteristically seems to have four cycles of 

 septa complete, with a fifth incomplete, decreasing in breadth 

 and height from the lower to the higher cycles, and varying 

 up to 1.5 mm. in exsertness, edges smooth, sides covered with 

 low, granular ridges radiating from the theca. The costae 

 equal the septa in number, and are subequal in size, very low 

 but distinct and granular. The intercostal valleys are generally 

 filled in below with epitheca, almost to the level of the top of 

 the costae, this deposition extending to within 2 or 3 mm. of the 

 thecal edge. Pali are present in front of septa of cycles I. to 

 III, before cycle I. round and before III. rough, flattened pillars 

 I mm. or so broad ; those before III. are more distant from the 

 centre of the cahcle, and with the pali of cycle II., typically form 

 chevrons before the secondary septa. Columella about i mm. 

 lower than the upper ends of the tertiary pali, formed by about 

 6 rods, which are with difficulty to be distinguished from the 

 pali of cycle I. 



