PROM THE AUSTRALIAN TERTIAR1ES. 



417 



was stated to be a fossil in the Mitchell-river Tertiaries by Mr. 

 Tenis on- Woods and myself, is a species of Glypeaster. The classifi- 

 catory position of the form I examined was a subject of doubt, as 

 will be gleaned from the following extract : — " Except in some slight 

 points in which there is great individual variation in the recent 

 forms, the fossil agrees with those which Gray called E. testudinarius 

 and E. australice, the latter of which has been absorbed by the 



former The species is interesting from its close resemblance to 



a Glypeaster ; but it has no pores close to the sutures of the plates 

 within the ambulacra on the actinal surface " *. 



M'Coy has shown that the internal structure of the test is that of a 

 Glypeaster, according to A. Agassiz, and he has investigated the 

 subject of the ambulacral pores and finds that they are variable ; 

 but probably that is produced by fossilization. 



Prof. M'Coy considers that the morphological distinction between 

 Glypeaster and Echinanilius, according to A. Agassiz, is barely suffi- 

 cient to separate the genera ; and it must be remembered that, with 

 the exception of the greater concavity of the actinal surface in 

 Echinanthus, the other structural differences are internal. The 

 specimen examined by Mr. Tenison Woods was not studied by me, 

 and Prof. M'Coy has not had the advantage of examining the very 

 large form which was noticed in my former communication, and 

 which is in the collection of this Society. It is exceedingly Echi- 

 nanthine in its general appearance, but the test is flat actinally for 

 some distance towards the deeply sunken peristome. The relative 

 measurements of Glypeaster gippslandicus, M'Coy, are : — length 

 90 millim.= 100, width 88, height 27. Those of the large form 

 now under consideration are : — length 105 millim.=100, width 85 - 7, 

 height 31. The suspicion that the two forms are not specifically 

 identical is somewhat aroused by the relative increase in length of 

 the larger form, and is intensified by the petals of the larger form 

 being much broader than those of the other ; moreover, the postero- 

 lateral petals of the Gippsland species are longer than those of the 

 larger form. If the drawing of the terminations of the petals given 

 by Prof. M'Coy is correct, there is almost, if not quite, a specific 

 difference between the forms, for the antero-lateral petals are tend- 

 ing to close, and are rather narrow externally, in the form which 

 came under my observation. In fact there is a facies about the 

 petaloid part of the test which recalls Glypeaster folium. Subject 

 to this expression of doubt, I agree with M'Coy in considering the 

 form to belong to his Glypeaster gippslandicus. 



In my former communication (p. 66) I expressed my belief in the 

 identity of Moiiostychia, Laube, and Arachnoides, Klein, mainly 

 owing to the furrowing of the ambulacra ; and the drawing and 

 description given by Laube of the internal supporting structures of the 

 test (Laube, "Eossil Echinoidea from the Murray Cliffs," Sitzungsb. 

 Akad. Wiss. Wien, vol. lix. Bd. i. 1869, p. 188, fig. 3 c). At 

 that time the reasons for separating the genus Monostychia from 

 Arachnoides were the not invariable supramarginal position of the 



* Quart. Journ. Geol. Soc. vol. xxxiii. (1877) p. 47. 



