82 



BRITISH PALAEOZOIC ASTEROZOA. 



The snpero-marginalia appear to form only a narrow. margin to the arm. This 

 appearance is partially because their inner extremities are covered by adradialia. 

 When the adradialia have fallen away, inner finger-shaped processes may be seen, 

 and the series looks much broader. The first pair of snpero-marginalia are larger 

 and more swollen than the remainder. Apart from tliis pair, there is little 

 differentiation in the series. 



Oral Surface (Plate III, fig. 1 ; Text-fig. 41). — The odontophor is large and 

 almost pear-shaped. Its distal end is not quite enclosed by the neighbouring 

 infero-marginalia. The species, therefore, can only be just passing out of the 

 " Hudsona^ter " stage. There is little differentiation among the infero-marginalia. 



40 41 



OppooP 



Text-fig. 40 (on left). — Plan of the apical surface of the disc and an arm of C'iractacasfer caractaci 



(based on 4/30(r). x 4. 

 Text-fig. 41 (on right). — Plan of the oral surface of one arm and the mouth-region of Caraclacasfer 



caraclaci (based on 4/30). x 4. 



The primitive condition of the species suggested by the position of the odon- 

 tophor, and the form of the infero-marginalia, is further emphasised by the 

 arrangement of the adambulacralia, which throughout the latter third of the arm 

 (ten plates) correspond in number to the infero-marginalia. In the proximal 

 portion of the arm there are fourteen adambulacralia corresponding to the first 

 eight infero-marginalia. 



The ossicles of the mouth-region are not well defined. Schuchert states 

 (p. 93) that " a peculiarity of this species is that the ambulacralia do not continue 

 round the axillary interbrachials, but cease with the basal inframarginals. There 

 are, therefore, in M. caractad no adarnbulacral oral armature spines." The 

 British Museum specimen examined by Schuchert presents this appearance, but 

 the specimens at Jermyn Street show the form to have the normal Asteroid 

 structure. The mouth-angle plates in these specimens are undoubtedly present 



1 



