2 



BRITISH FOSSILS. 



of the disk dorsally is covered with small irregular and pentagonal 

 punctated flat plates, those towards the centre of the rays arranged in a 

 more or less distinct series. Similar ossicula occupy the interambulacral 

 spaces beneath. The ambulacra are bordered by quadrate stout plates 

 of moderate dimensions, furrowed on their surfaces by three or four 

 strongly marked longitudinal grooves, which are the lodging-places of 

 small ambulacral spines. 



This species must have attained considerable dimensions. The largest 

 fragment figured (1, would indicate a star-fish measuring at least 

 8 inches from the extremity of one arm to the end of that most distant, of 

 which 2 J inches would go to the disk. The marginal plates in this specimen 

 measure 3-16ths of an inch across, and nearly as much high. The num- 

 ber of marginal plates in a full-grown specimen was probably about 

 28 on either side of each produced angle. 



Locality and Geological Position. — Goniaster Stokesii occurs not 

 unfrequently in the London clay of Sheppey. The specimens figured 

 were communicated to the Geological Survey by Mr. Charles Stokes, 

 and Mr. Bowerbank possesses a number of fragments of the same spe- 

 cies. The peculiar convex, nodulose marginal plates, conspicuously 

 distinguish it from any other tertiary star-fish. 



Fig. 2. 



GONIASTER MARGINATUS. 



E. Forbes, in " Memoirs of the Geological Survey of Great Britain," 

 vol. ii. part 2, p. 475. 



Diagnosis. G. carp ore? <■ — ossiculis later aJibus disci magnis., ohlongis, 

 convexiusculis, rugoso^punctatis, marginatis ; margine elevate. 



Description. — All that we possess of this species is a fragment, con- 

 sisting of five superior and as many inferior marginal plates, which, 

 however, present characters so distinct that they cannot belong to any 

 other described tertiary star-fish. The superior plates are large, oblong, 

 regularly declining outwardly, and low-sided. Their surface is but 

 slightly convex, thickly punctured all over, and bordered laterally by a 

 distinct elevated rim. The inferior plates are similar, but have even 

 more elevated margins, and the rim is continued on them across their 

 outer sides. What few body plates are visible are small and punctate. 

 The fragment measures one inch and one-eighth in length. The largest 

 plate is three-eighths of an inch in length, and less than two-eighths at 

 its broadest part. 



Locality and Geological Position. — The specimen is from the London 

 clay of Sheppey, and was communicated to the Geological Survey by 

 Mr, C. Stokes. 



