L92 CEYLON PEARL OYSTER REPORT. 



from the rounded base to the top of a primary septum. The calice is subcircular, 

 measuring 35 millims. in its longer and 33 millims. in its shorter diameter. The 

 columella is oval, measuring 10 millims. X 6 millims., and has a horizontal surface. 

 The specimen was evidently fixed in early life and has become detached, the scar of 

 detachment being healed over in a peculiar manner by the continuation of sixteen 

 costas round the bottom of the corallum, to meet and fuse with their fellows of the 

 opposite side. These costse belong to the septal systems at either end of the longer 

 axis of the calice ; the costse of the lateral systems converge below and unite to form 

 two somewhat irregular and not very conspicuous lateral basal prominences. The 

 specimen was completely covered by soft tissues, but these had to be removed to 

 facilitate the study of the corallum. 



I have been unable to refer this specimen to any known genus, and have therefore 

 made the new genus Rhodocyathus to contain it. The name is descriptive of the 

 shape of the calice, which bears a resemblance to a conventional rose. It differs from 

 all the members of Duncan's Turbinoloida in the characters of the columella. It is 

 distinguished from the majority of the Trochocyathoid alliance by the absence of pali, 

 and its shape and the character of its septa and costse mark it off from the somewhat 

 vague and all-embracing genus Ceratotrochus, as defined by Duncan. It cannot be 

 placed in any genus of the Discocyathoid alliance, nor yet among the Haplophylloida. 

 The presence of a columella separates it from all the Smilotrochoida ; the character 

 of the columella prevents its being placed among the Placotrochoida ; and it certainly 

 is not a Flabelloid. The genus shows most affinity to Ceratotrochus and Delto- 

 cyathus, and may be described as a Trochocyathoid without pali. 



Cyathotrochus, n. gen. 



Corallum simple, free, without a trace of adherence, forming a short, laterally 

 compressed cone. Costse moderately prominent near the lip of the calice, but scarcely 

 distinguishable below and indistinguishable near the bluntly pointed base ; the 

 primary and secondary costse somewhat more prominent than the tertiaries, which in 

 turn are rather more prominent than the quaternaries ; the costse corresponding to 

 the primary septum at each end of the longer axis of the calice much more prominent 

 than the rest and continued as sharp ridges about half-way down the corallum, but 

 not forming aliform expansions. Calice elliptical, subplane. Columella essential, 

 with a papillary upper surface, projecting slightly in the calice. Septa in six systems 

 and four regular cycles ; the primary and secondary septa subequal, moderately 

 exsert, arched above, with nearly vertical inner margins, their surfaces ornamented 

 with rows of relatively large granules, arranged nearly parallel to the inner margins. 

 Paliform lobes, separated from the septa by a deep but narrow notch, stand in front 

 of the first three cycles of septa and connect them with the columella ; those in 

 front of the tertiaries are the largest, but they do not form chevrons or deltas. 



