PALASTERINA ANTTQUA. 



233 



P. bonneyi, but neither he nor other authors appear to have recognised that the 

 specimen was the " P. primaevus " of Salter. The form has been somewhat 

 distorted by post-mortem pressure. Specimen 40301 shows the apical surface only. 



Oral Surface (PL XVI, fig. 2; Text-fig. 168).— The groove has been forced 

 widely open and in consequence appears to be shallow. The ambulacralia are 

 exposed in full length. They are opposite or slightly alternating in the proximal 

 region, distinctly alternating distally, and have the usual structure associated 

 with these primitive forms. The small size of the adambulacralia makes their 

 ornament difficult to determine. So far as one can see, there was no distinct 

 adambulacral ridge, but the spines seem to have been distributed all over the face 

 of the ossicle. The majority of the spines appear to have been long. 



The mouth-angle plates look like poorly preserved smaller editions of the 

 corresponding structures in /'. yrims&va. 



S.M. 



Text-fig. 169.— Drawing of a small portion of theapical surface of an arm of Patasterina antiqua (=P. bonneyi). 

 In.M., inter- marginalia ; B., radial; S.M., supero marginal ; *.„ adradial. x 20. 



The interradial areas are much more extensive than in P. primasva, but the 

 extent varies so much in the different radii (PI. XVI, fig. 2) that one can only 

 suppose that the body was considerably swollen during life, and that the plates now 

 seen on the oral surface once formed the lateral interradial walls of the disc. The 

 plates are not pavement-like, as in Gregory's figures, but rounded. Some show 

 rounded articulations for spines. A plate shaded in the figure may represent the 

 madreporite, but one cannot be certain of the madreporiform markings. 



Apical Surface (PI. XVI, fig. 1 ; Text-fig. 169). — The apical surface is so very 

 like that of P. primxva that I do not consider it necessary to figure it in detail. 

 One must note, however, that certain of the plates in the centre of the disc which 

 are visible in the photograph, and have been previously figured as disc plates, 

 are really the mouth-angle plates pushed through the apical covering after death. 

 Adradialia are more numerous than is usual in P. primaeva, but this one would 

 expect because of the swollen nature of the arms. 



