Victorian Fossiis, Part XIX. 77 



DESCRIPTION OF THE SPECIES. 



Fain. ACMAEIDAE. 



Genus Helcionopsis, Ulrich and Scofield. 

 Helcionojysis nycteis, Cresswell sp. (Plate II., Fig. 1). 



Tryhlidium. iiycteis, Cresswell, 1893. Proc. Roy. Soc. Victoria,, 

 vol V. (N.S.), p. 41, pi. IX., fig. 4. 



Capidus nycteis, Cresswell sp., Chapman, 1913. Rep. Austr. 

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



Description. — Shell sul>ovate, strongly convex along the back, 

 broadening and expanding towards the sides. Form resembling a 

 strongly-arched Crepidida. Apex slightly overhanging the pre- 

 apertural area. Side view plano-convex, highest at the middle 

 point between the apex and ventral edge. End view semi-ovate, 

 W'ith a slight cant towards one side. Lines of growth marked by 

 numerous raised concentric ridges, the interspaces relieved by radial 

 striae. Lines of growth in middle of shell about .5 mm. apart. 



Dimensions. — Holotype. Length, 31 mm. ; greatest width, 20' 

 mm. ; height, from back of shell to ventral edge, 15 mm. 



Observations. — This shell was originally referred to Tryhlidium 

 by Mr. Cresswell on account of its resemblance to some Gotland 

 forms described by Lindstrom. The Gotland specimens ai-e more 

 depressed, with the exception of one species, referred doubtfully to- 

 Tryhlidium,^ and which appears to l>elong to Helcionopsis, and some- 

 what related to the above species. 



The present writer referred this species to Capidus in 1913, on 

 account of the asymmetrical apex, but in the light of the structure 

 shown in the next species described, the relationship appears to he- 

 with Helcionopsis. 



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

 Lilydale. Holotype presented by the Rev. A. W. Cresswell, M.A. 



Helcionopsis elegaiduhim, sp. nov. (Plate II., Figs. 2, 3; Plate VI., 

 Fig. 49). 



Description. — Shell sub-ovate, one and a-half times as long as. 

 broad; apex acuminate but not prominent; sides gently rounded, 

 back highly arched near apex and depressed convex near ventral 

 border. Growth-lines lamellate and situated about 1.5 mm. apart 

 in the middle of the shell; interspaces marked with numerous radial 



1 (I) Tryhlidium radiatum,UndstT6m. Kongrl. Svenska Vet.-Akarl. Handl., Bd. xix., No. 6,. 

 1884, p. 58, pi. xviii.,figs. 1, 2. 



