104 Frederick GhapriKin : 



seen in Chonetes and Sfrophnlosin, to -wliicli tliis peuns, at least in 

 its young stages, shows marked affinities. It is nioru tliun pinljable 

 from the above structural features that Leptaeua is of a more 

 advanced type of the Strophomenidae, which shows retrogressive 

 tendencies in its later development. 



Occurrence. — The above species, L. rhoinhoUJalh, has l:)een 

 recorded from one doubtful Melbournian locality, Eraser's Creek, 

 Springfield; otherwise, it is restricted in Victoria to the Yeringian 

 stage, occurring at Lilydale, Croydon, Loyola and the Thomson 

 River. It also occurs in the passage beds (between Melbournian and 

 Yeringian) at Whittlesea. 



The unique specimens showing the spiralia and brachial supports, 

 as well as the example with finely denticulate hinge-line, were found 

 by Mr. Geo. Sweet, F.G.S. at Loyola, near Mansfield, who has 

 presented them to the Museum. 



Leptaena rhomboidalis, Wilckens sp. ; var. un data,. McCoy. 



Orthis undata, McCoy, 1846, Syn. Sil. Foss., Ireland, p. 136, pi. 

 iii., fig. 1. Lejytaena deltoidea Conrad, var. undata, McCoy, 1852, 

 Brit. Pal. Foss., p. 234, pi. IH.. figs. 38, 39. Strophomena 

 deltoidea, Conrad sp., var. undafa, McCoy, Davidson, 1871, Mon. 

 Sil. Brach. (Pal. Soc), pt. vii.. No. 4, p. 295, pi. xxxix., figs. 23, 

 24. L. rhomboidalis, Wilckens sp. var. undata. McCoy, Chapman, 

 1907, Vict. Nat., vol. xxii., p. 239. 



The characteristic ripple-surfaced shell of the above form is met 

 with in various stages of development, from 35 to nearly 100 nnn. 

 in width, in the Victorian Silurian. It appears to keep tolerably 

 distinct from L. rhomhoidalis by its more transverse shape, larger 

 size and irregular and persistently wrinkled surface; and it may 

 therefore be regarded as a tolerably well-marked variety of L. rhom- 

 hoidalis 



Occurrence. — Silurian (Yeringian). Loyola, near Mansfield, in 

 hard, brown and grey mudstone. Collected by Geo. Sweet, Esq., 

 F.G.S. 



Fam. PiJourcTiDAK. 



Geiiu.s Chonetes, Kischer. 



(']ioiietf!< hipartita. sp. iiov. Plate X., figs. 8-10. 



Descri pt'ioii . — Slic'll small, si'niicircular or t raiisviTsc. Pedicle 

 valve strojigly convex; median aii-a conspicuously arelicd and 

 medially sukate ; l)eak ])rominent; area. on either side of median 



