94 Frederick Chapman : 



Occurrence. — Silurian ( Verin<i;ian). In limestone. Cave Hill, 

 Lilydale. In brown niudstone. junction of the Woori-Yalloc-k and 

 Yarra; Geol. S. Vict. B23. 



Scnlaefrochus lindsiroeini, Etheridge fil. sp. 



Trod/ us (Scalaefrochus) lirulKfroemi, K. Etheridge, jnr., 1890 

 Rec. Aust. Mus., vol. I., No. 3, p. 66, pi. VIII., figs. 1. 2. Chap- 

 man, 1913. Rep. Aust. Assoc. Adv. Sci., vol. XIV., p. 228. 



Observations. — The high spiral and angulate sutural margins 

 serve to separate this form from .S". antiquum. It is fairly common 

 in the Lilydale limestone, but lias not yet occurred elsewhere, 

 although an indeterminate form of the genus has been noted by me 

 from Yeringian beds at Marble Creek, Gippsland.i 



Occurrence. — Silurian (Yeringian). In limestone, Cave Hill, 

 Lilydale. 



Fam. TllOCHONEMATlDAK. 



Genus Cyclonema, J. Hall. 

 Cyclonema lilydalensis, Etheridge til. (Plate V., Fig. 38). 



Cyclonema lilydalensis, Etheridge, jnr., 1891. Rec. Aust. Mus., 

 vol. I., No. 7, p. 128, pi. XIX , fig. 3. 



Observations.— In the collection of the National Museum there is 

 a fair number of quite small specimens of Cyclonema. As it had 

 been suggested that these probably represent a new species, it is 

 worth putting on record my conclusions regarding them. These 

 small forms consist of about five whorls. The sides of the volutions 

 are rounded, but as a rule the whorls are rather depressed, though 

 occasionally the spire is fairly high, as in C. australis."^ The 

 ornament is exactly similar to that in full-grown specimens of 

 C. lilydalensis, and when the number of whorls is taken into 

 ■consideration, there being from four to six in the small sliells, and 

 ■eight in the fully developed ones, it Avill be seen that there is no 

 ground for their separation. Further than this, a series of 

 Cyclonema in the Dennant collection shows all gradations fi'om the 

 immature to the adult condition. The increase in size of the 

 later whorls is very rapid, the height of a six-whorled shell being 

 14 mm., and an eight-whorled shell, 42 mm. Mr. Etheridge, in 

 giving the number of whorls as six in C. australis, states that 

 <C. lilydalensis has a much larger number. 



1 Reo. Geol. Surv. yict., vol. ii., pt. i., 1907, pp. 11, 17. 



2 Kec. Austr. Mus., vol. i., No. 3, 1S90, p. t>3, pi. ix., figs. 4, 5. 



