PROMO PAL.E ASTER ELIZ^. 



93 



Specific Characters. — Interbrachial area consists of one pair of inf ero-marginalia 

 and the odontophor. 



Apical Surface (PL IV, figs. 1-4; Text-figs. 51-54).^ — ^Practically all the 

 casts show considerable disturbance of the ossicles after entombment. Further, 

 the best preserved specimen was collected in a fragmentary condition, and the 

 pieces have been glued together. Unfortunately, some of the cracks go across the 

 disc and add to the difficulties of study. In consequence of these many imper- 

 fections, I have not attempted to give a complete restoration of the form and have 

 only figured those portions of the surface which appeared capable of reasonable 

 interpretation. The ossicles of the disc have been least disturbed in the specimens 

 D. 32 and D. 95c. The cast of D. 32 suggests that the centre of the disc was 

 occupied by a circlet of five plates of medium size. Apparently each of these was 



51 



53 



Text-fig. 51 (on left). — Diagram of disc and base of arm of Prunwpalaaster elizm (based on D. 32 and 



D. 215). X G. 

 Text-fio. 52 (on right). — Oiitline drawing of ossicles on apical surface of base of an arm of Promo- 



palceaster eliza (taken from D. 215). 



surmounted by a single large spine, for two such spines may be plainly seen. These 

 have fallen over and hidden the place where one might expect to find a centrale. 



The second set of ossicles which help to guide the eye in the study of the apical 

 region are the supero-marginalia. These are readily recognisable in the majority 

 of the specimens. The most proximal members of the series do not margin the 

 disc, but are thrust apexwards by the development of a very conspicuous inter- 

 marginal area. As is usual in such cases, the proximal supero-marginalia are 

 rather smaller than the succeeding marginalia at the base of the arms. 



Small but conspicuous primary interradialia are to be seen at the point of 

 junction of the supero-marginalia of opposite arms. A large rounded madreporite 

 (Text-fig. 54) is seen in D. 32 and D. 104. It is not visible in the remaining 

 specimens, possibly because of post-mortem disturbance and loss. It is to be 

 noticed that the development of the large intermarginal area has forced the 

 primary interradialia well into the middle of the disc. The madreporite, which is 

 associated by origin (see p. 40) with a primary interradial, has in consequence 



