52 FOSSIL ASTEROIDEA. 



This species was described by the late Professor Edward Forbes in Dixon's 

 ' Geology of Sussex ' in 1850 in the following words : 



" Body pentagonal, with gently lunated sides. Superior intermediate marginal 

 plates four, nearly equal, plain, smooth, or minutely punctate. Inferiors similar. 

 Superior oculars mitrate, large, triangular, acuminated. Ossicula of disc punc- 

 tate. 



" Easily distinguished from the last species [imcahis] by its flattened mar- 

 ginals and from the next [Hunteri] by its lunated sides. 



" Mus. Bowerbank, from the white chalk ; also in the collection of the 

 Geological Survey" (op. cit., p. 331). 



No figure of the species has ever been published, and no record exists as to 

 the specimen or specimens seen or used by Forbes as type. I have been unable to 

 find any example from the Bowerbank Collection to which this name has been or can 

 be applied; and the only examples which I have seen referred to this species at all 

 are four fragmentary specimens now preserved in the Museum of the Geological 

 Survey in Jermyn Street, and not more than two of these could have been in that 

 collection in 1850. 



After a careful study of these specimens I am bound to confess that 1 find no 

 character by which they can be separated from Metoimster uncatus ; and if the 

 diagnosis is correct I am led to consider that I have certainly not seen Forbes's 

 type. The sw^ero-marginal plates in the specimens in question are not flattened, 

 and cannot be said to differ in character from those of Metopaster tmcatus. 



A possible explanation suggests itself in the supposition that Forbes inad- 

 vertently mistook the actinal for the abactinal surface of the disk, a mistake which 

 might easily be made by a less careful observer than the author of this species 

 when dealing with a badly preserved fragment. If, however, what is really the 

 actinal surface has been described as the abactinal surface the difficulty is prac- 

 tically solved, for the infero-marginal plates in the fragments under notice are 

 " plain, smooth, or minutely punctate." That this is not an improbable explanation 

 I would submit the following facts : — (1) that in the original diagnosis of 1848^ 

 Forbes states that the infero-marginal plates are unknown ; (2) that in the 

 diagnosis of 1850, given above, the infero-marginal plates are stated to be 

 " similar " (to the supero-marginals) ; and (3) that notwithstanding these state- 

 ments all the examples in the Geological Survey Collection are essentially actinal 

 presentments of the disk, and therefore the infero-marginal plates are the plates 



1 The following is the diagnosis iu full : — " G. corpore pentagonali, lateribus lunatis ; ossiculis 

 lateralihus superioribus 4, subsequalibus, planis, minutissime punctatis ; inferioribus ? Ossiculis 

 oeularihus superiorihus magnis, triaugularibus, mitratiB, tumidis, acuminatis." (' Mem. Geological 

 Survey of Great Britain,' vol. ii, p. 472.) 



