CARACTACASTER CARACTACI. 81 



1899. Palieaster caradaci, Gregory, Geol. Mag., dec. 4, vol. vi, p. 344. 



1910. „ ,, Sclioudorf, Jahrb. uassauiseh. Ver. Naturk., Wiesbaden, vol. Ixiii, p. 227. 



1913. Protopalasasfer caradaci, Spencer, Introductory Section to this Monograph, pp. 21, 30. 



1914. Mesopalieaster caradaci, Schuchert, Fossilium Catalogus, Animalia, pt. 3, Stelleroidea palseozoica, 



p. 24. 



1915. „ „ Schuchert, Bull. 88, U.S. Nat. Mus., pp. 92, 93, pi. 9, fig. 6 ; pi. 11, 



fig. 1. 



Material. — There are four specimens in the Museum of Practical Greology, 

 Jermyn Street (ISos. 4/30, 4/30^7, 4/35a, 4/36), each possessing both imprint and 

 counterpart. A fifth specimen, also consisting of imprint and counterpart, in the 

 British Museum (Nat. Hist.) (No. E. 48206), is the holotype of the species. 



Apical Surface (Plate II, fig. 4; Text-fig. 40). — Moulds taken from four 

 specimens (Nos. 4/30, 4/30(^ 4/35o. and E. 48206) show the apical surface. 

 Unfortunately, the matrix in which the original fossils were embedded was some- 

 what coarse, and as the plates are not swollen one does not obtain sharp casts. In 

 consequence it is only by careful examination and comparison of the different 

 specimens that the structure can be elucidated. 



The central portion of the disc at first sight appears to have been especially 

 badly preserved. Possibly the want of evidence of clear-cut ossicles in this region 

 is due to the fact that originally the disc was covered with a leathery skin 

 in which the ossicles were somewhat loosely embedded. My restoration (Text- 

 fig. 40) is based upon the assumption that there were three rather loose circlets of 

 intermediate plates around the centrale, a view suggested by the first three speci- 

 mens referred to above. The primary radialia and interradialia are also not very 

 conspicuous ossicles, although both series are readily recognisable. The primary 

 radialia are large compared with the succeeding radialia, but they are flat, and do 

 not stand out. They have the usual breastplate-shaped form. The primary 

 interradialia are small plates situated just proximal to the supero-marginalia. Just 

 behind the primary interradial, on the left side of the figure, is situate a plate which 

 must have been the madreporite. Unfortunately the coarse-grained sandstone has 

 not preserved the madreporiform markings. 



Nearly all the radialia are elongated and cut away at their edges. It is only at 

 the extremities of the arms that they become irregularly polygonal in shape and 

 closely touching. 



There is a single row of adradialia on each side of the radialia, but the impres- 

 sions of these ossicles are poor. One of the arms of 4/35a shows that in the 

 proximal region the radialia and adradialia were equal in number. Several of the 

 arms of the other specimens suggest that there were twice as many adradialia 

 as radialia, as shown in Text-fig. 40. It is possible that the apparent doubling of 

 the adradialia is due to Aveathering of the surface of the ossicles, but the appear- 



ance is so regular as to suggest that the arrangement was natural. 



11 



