REVISION OF PALEOZOIC STELLEROIDEA. 171 



Ambulacrals in two columns, opposite, short but mde, and about 

 as numerous as the adambulacrals. Podial openings unknown. 



Genoholotype. — Palxaster clarkei De Koninck. This is also the only 

 species of Monaster and occurs in the ''Upper and Lower Marine 

 series" of the " Permo-Carbonif erous " of New South Wales. 



RemarTcs. — ]\lr. Ethcridge proposed Monaster as a subgenus of 

 Palseaster, from which it differs so radically as to give it easily the 

 rank of a genus. He defines the group as follows: In Palseaster 'Hhe 

 adambulacral plates, bordering the ambulacral avenues, are small 

 and quadrangular, followed by large transverse marginal plates. In 

 our Permo-Carboniferous species, on the contrary the adambulacral 

 plates are transversely elongated, and occupy nearly the whole of 

 the actinal surface on each side the avenues. The marginal plates 

 [having reference to the plates along the margins which consist of 

 adambulacrals, and also form part of the abactinal skeleton], in con- 

 tradistinction to those of Hall's Silurian species, are here smaller and 

 subdorsal in position. The question now presents itself, of what value 

 in a classificatory sense is this character ? Hall lays particular stress 

 on the position of these plates on the actinal side of Palxaster. He 

 says it 'has two ranges of plates on each side of the ambulacral 

 groove; marginal [inframarginal] and adambulacral plates on the 

 lower side, besides ambulacral or poral plates. The upper or dorsal 

 side has three or more ranges of plates.' In the case of our specimens, 

 only one set of plates, excepting those of the ambulacral grooves, 

 are, as before stated, absolutely actinal; the marginals [same usage 

 as before] arc strictly so, or, at the least sub-dorsal. Under these cu- 

 cumstances, I purpose distinguishing our Australian species under 

 the subgencric name of Monaster (from the one or single row of 

 adambulacral plates on each side of an ambulacral avenue)." 



The original definition is hero given at length to show that it can 

 only apply to the structure in Palseaster clarJcei De Koninck, which 

 is also the first species following the generic discussion. The author 

 in the same work describes a new species which he also refers to 

 Monaster, Palseaster (Monaster) giganteus, but its structure is radi- 

 cally different and does not conform with the subgeneric definition 

 by Etheridge. Elsewhere in this work it is taken as the genotype of 

 the now genus Australaster. Gregory in the serial above cited takes 

 as the genotype of Monaster the last named species, the third of 

 Etheridge, and transposes the former as the genotype to his new 

 genus Eilieridgaster. This the writer holds can not be done even 

 though Etheridge selected no genotype for Monaster. That author's 

 genotype, as the name implies, refers to a species with but a single 

 column of plates on each side of the ambulacrum. The species selected 

 by a subsequent author should have the structure impHed in the 



