190 Miscellaneous. 



material of the Iowau fossils by silica has taken place only in certain 

 parts, forming a number of siliceous boxes, as it were, which are 

 eitber hollow or more or less filled with chalcedony or crypto- 

 crystalline silica. They are therefore neither casts nor impressions, 

 and details of structure are frequently destroyed. 



Petalocrinas is shown to have a dicyclic base — not monocyclic, as 

 originally described. The structure of the tegmen is shown to be 

 that of the Cyathocrinoidea. The arm-fans characteristic of the 

 genus are proved to have been formed by fusion of the branches of 

 an arm of Cyathocrinid type. In them, description is given for the 

 first time of axial canals, covering-plates, the articular facet, and 

 various minor structures. The species P. major, Weller, is sbown 

 to be an Omphyma ; but P. mirabilis, Weller, the genotype, is 

 redescribed, and with it five new species — two from Iowa ; three, as 

 well as a possible mutation of one of them, from Gotland. A family 

 Petalocrinidae, descended from the Cyathocrinidae, probably by way 

 of Arachnocrinus, is founded for the reception of this genus. 



MISCELLANEOUS. 

 The Generic Name Thylacomys. By Edgar R. Waitk. 



Since revising the proofs of my article " Observations on Muridie 

 from Central Australia " *, I find that the name Thylacomys may 

 be in jeopardy. Though not contained in the classic catalogues of 

 Agassiz and Scudder, and therefore apparently available, it has yet 

 made an appearance, if an accidental one, in literature. 



A footnote in the 'British Museum Catalogue of Marsupialia' 

 (pp. 221-222) reads as follows :— « Blyth (Cuv. An. K. p. 104, 

 1840) states that Prof. Owen had separated off ' The Philander, 

 Perameles lagotis? as a genus under the name of Thylacomys. I am, 

 however, quite unable to find any distinction of the genus in 

 Prof. Owen's papers, and therefore retain the well-known name 

 [Peragale~] given to the genus by Gray. Blyth's statement was, 

 perhaps, based on a confused account of Gray's Thylamys elegans 

 ( = Dklelphys elegans), a member of the group of Opossums to which 

 the latter author applied the name of ' Philander.' " 



I am unable to verify Thomas's quotation in tbe original (1840) 

 edition ; but in the only two editions available to me, namely 1849 

 (p. 104) and 1863 (p. 92), the genus is rendered Thalacomys, not 

 Thylacomys. 



Australian Museum, Sydney, 

 10th May, 1898. 



• Proc. Roy. Soc. Victoria, x. (new series) 1898, pp. 114-128. 



