90 Frederick Chapman : 



Occurrence. — Silurian (Yeringian). Apparently fairly common. 

 • in the newer Silurian. Holotype, in mudstone from KiUara, near 

 Seville, Upper Yarra district; presented by Mr. J. S. Green. 

 Paratype, from brown mudstone, Loyola, near Mansfield; presented 

 by Mr. G. Sweet, F.G.S. 



EuompJialiis northi , Etheridge fil. sp. 



Oriostoma northi, II. Etheridge, jnr., 1890. Rec. Aust. Mus., 

 vol. I., No. 3, p. 64, pi. IX., figs. 6, 7. 



Exiomphalus northi, Eth., fil. sp.. Chapman, 1913. Rep. Aust. 

 Assoc. Adv. Sci., vol. XIV., p. 227. 



Observations. — The nearly equilateral spiral form of the shell 

 and the concave external face of the umbilicus show the relation- 

 ship of the above species to be Avith Euowphalus. 



The operculum in Oriostoma has a convex or conical exterior,, 

 whilst in Euomjyhaliis northi it is concave. 



Examples in the brephic to neanic stages exhibit a smoother shell 

 than the adult form. 



Occurrence. — Silurina (Yeringian). Numerous specimens in lime- 

 stone, Cave Hill, Lilydale. One fine example with the operculum in 

 situ, was presented by the Rev. A. W. Cresswell, M.A. * 



Genus Liomphalus, gen. nov. 



Definition. — Shell discoidal, widely umbilicate and biconcave;, 

 whorls smooth and sometimes obscurely keeled along the back. 

 Earlier whorls consisting of a thin shelled series, followed by two or 

 more stout whorls, either closely adpressed or free in the later 

 portion. Early part of series divided into chambers as in Etiom- 

 phalus and Strajiarollus (S. dionysii, Montf.). Aperture elliptical 

 or angularly ovate. Type, Liomphalus australis. The genus 

 includes Euomphalus disjiinctus, J. Hall, E . (StraparoUus) clyme- 

 nioides, J. Hall. E. triquetrus, Lindstrom, and E. gotlandicus, 

 Lindstrom. 



This generic type may be distinguished from Enomphalus, 

 Sowerby (sensu stricto) in having smooth, rounded or uniangulate 

 whorls ; and from StraparoUus, Montfort, in having a concave- 

 spire; whilst from Lytospira, Koken, it differs in the more closely 

 coiled shell, and in the absence of a scaly ornament. 



Name derived from leios, smooth, and omphalos, an umbilicus. 



Liomphalus australis, sp. nov. (Plate IV., Figs., 32, 33). 

 Description. — Shell moderately large, discoid, compressed. Spire- 

 somewhat concave, umbilical suiface rather deeply concave, consist- 



