K. KOMEYAMAI. — GEN. CHAKACTEES. -Oo 



tlie diameter increases up to 75-87 mm. at about tlie middle. 

 Thence upwards the body again gradually narrows to the region 

 just behind the cufiF, where the diameters measures 34-37 mm. 



The superior end may be called truncate, not rounded. 

 Cross-section of the body presents an irregularly circular outline. 

 The wall is 2-5 mm., at places only 1 mm., thick. 



The superior terminal osculum is 27-30 mm. in diameter. 

 The entrance into it is guarded by a spicular wreath of corona 

 as efficiently as by a sieve-plate. 



The corona (PI. IX, fig. 3) is composed of strong, straight 

 or slightly curved, shai'ply pointed, spicular raj's, which freely 

 project out in a row froui the angular oscular edge and stand 

 out obliquely upward and iuward to a length of 18 mm. or less. 

 I count 30 coronal rays in all ; at the roots the intervals be- 

 tween them are about 2'/2 mm. on the average. To the naked 

 eye the rays present a peculiarly glistening appearance, which is 

 due to the rough shagreen-like nature of their surface. Looking 

 at the corona from above, its inwardly directed rays are seen 

 arranged like the spokes of a wheel, leaving in the center but a 

 narrow, free passage between their points. 



A coronal wreath of similar appearance has been known from 

 Twfjcria pulchra described by F. E. Schulze in the Challenger 

 Report ('87). The same was later assumed by him ('95, p. 35) 

 to have been mechanically produced by the accidental loss of the 

 central part of a sieve-plate, such as is possessed by Dictyaulus 

 elcgam. Whatever be its nature in T. pulchra, the corona in R. 

 okinoseana is a perfectly natural feature. There can be no doubt 

 about this not only from the presence of it in the second 

 specimen, but also from the facts : 1) that the rays are invaria- 



