82 Frederick Chapman : 



in number, subaugulate and rounded, more convex Ijeluw than 

 above. Slit band prominent, projecting beyond the contour of the 

 whorls, and bounded above and below by a raised border ; surface 

 gently concave, with four crescentie growth-lines in a millimetre. 

 Base moderately convex; umbilicus open. Mouth, subovate. Surface 

 of whorls traversed by close and fine growth-lines, curving back- 

 Avards to the band above, with a sigmoidal forward and backward 

 curve below. Fine cross-lines between growth-lines visible in a 

 strong light. 



Dimensiom. — Height about 27 mm. Width at base about .30 mm. 

 Height of body whorl, 18 mm. Width of slit-band, 1 mm. Most 

 of the specimens are more or less distorted, but being fairly 

 numerous, an accurate average idea may be fornied of the dimen- 

 sions. 



Observations. — This striking species is not far removed from 

 McCoy's P. crenukita, from the Upper Ludlow, of Brigsteei-, Kendal, 

 Westmoreland.^ It differs in the larger numl^er of whorls, in their 

 more depressed contour and in the less deeply incised suture ; more- 

 over, the band in P. maccoyi is not concave as in the English 

 species. 



Another closely related form is Lindstrom's P. chiustrafa,- from 

 the Wenlockian, of Gotland, which resembles the Victorian species 

 in proportionate height and width, in the number of whorls and 

 in the general ornament, with the specific difference that the growth- 

 lines on the whorls of P. rnaccoyi have a distinctly sigmoidal sweep, 

 whereas in P. claustrata they are more gently curved. The latter 

 form also has a more excavated slit-band. 



The above described examples of P. rnaccoyi were selected many, 

 years ago by McCoy from a collection of Survey fossils, and placed in 

 the Museum under the name of Pleuroiomaria, but without further 

 reference. The species is now identified Avith his name in honour 

 of his classical work on the gasteropods of the British palaeozoic 

 system. 



Occurrence. — Silurian (Yeringian). Moderately common in olive- 

 brown and blue mudstone, from the junction of the Woori-Yallock 

 and Yarra, Upper Yarra district. G.S.V. (B2.3). 



Genus Mourlonia, de Koninck. 

 Mourlonia duni, Etheridge fil. 



Mourlonia duni, Etheridge, jnr., 1898. Rec. Austr. Mus., vol. 

 III., No. 4, p. 73, pi. XV., fig. 5; pi. XVI., fig. 2. 



1 Brit Pal. Foss., 1855, pt. ii., p. 291, pi. i., k, fi^. 45. 



2 KoiiKl. Svenska Vet.-Akad. Handl., Bd. xix., No. 6, 1884, p. 97, pi. vii., fi','s. 31-36. 



