﻿CALLIDERMA MOSAICUM. 11 



in diameter. The remaining plates which occupy the intermediate areas are 

 tetragonal or rhomboid. All the plates have their surface marked with rather 

 widely-spaced punctations — the impressions of the granules previously present. 

 Small foraminate pedicellariee are also frequently present here and there, usually 

 near the margin of the plate. 



The madreporiform body is flat, distinct, and polygonal in outline ; it is situated 

 near the centre of the disk. Its surface is marked by fine straight strias, which 

 radiate regularly centrifugally from the centre to the margin (see PL V, fig. 2 e). 



Other specimens show that the infero-marginal plates in this species are more 

 nearly subequal to the supero-marginal series than in Galliderma Smithise, that the 

 actinal intermediate plates are relatively larger than in that species and a good 

 deal larger than the abactinal paxillar plates or tabula. The actinal intermediate 

 plates originally bore granules only, judging from the character of the punctations 

 with which their surface is ornamented. A fragment belonging to the British 

 Museum Collection (which bears the register number " B 373 "), in which the spines 

 that formed the armature of the adambulacral plates are preserved, indicates that 

 these spines are smaller, shorter, and perhaps more numerous than in Galliderma 

 Smithise. 



In the example drawn on PL VI, fig. 2 a, the supero-marginal plates are pre- 

 served, but the whole of the abactinal plating has been removed, leaving exposed 

 the inner surface of some of the actinal intermediate plates and the adambulacral 

 plates. Magnified details of these plates are given, and they represent the cha- 

 racters of the structures preserved better than any verbal description. 



Dimensions. — The large example figured on PL V, fig. 2 a, has the following 

 measurements: — Major radius 82 + mm. (all the rays are broken and imperfect, 

 and the full dimensions cannot therefore be given) ; minor radius 36 mm. ; thick- 

 ness of the margin about 8 mm. Breadth of a ray between the eighth and ninth 

 supero-marginal plates about 15 mm., or a trifle more. 



Locality and Stratigraphical Position. — The example figured on PL V, fig. 2 a, 

 is labelled from the Lower Chalk, but the locality is not recorded. It formed 

 part of one of the old collections preserved in the British Museum. Other 

 examples in the British Museum are from the Grey Chalk or Chalk Marl of Dover, 

 from the Lower Chalk of Glynde in Sussex, and from the Lower Chalk of 

 Amberley Pit, Arundel. There is also a magnificent specimen in the Museum of 

 Practical Geology, Jermyn Street, from the Lower Chalk of Dover. 



