76 Proceedings of the Royal Society of Victoria. 



concavity of the brachial valve, and in the larger number of 

 radii. 



Occurrence. — -In the brown and blue hardened clays of Mel- 

 bourne ; South Yarra Improvements [634-8] ; South Yarra 

 sewerage tunnel, Domain Road, presented by Mr. F. Spry [630-3]; 

 sewerage tunnel near the Old Fish Market, Flinders Street 

 [1419]; sewerage tunnel, Swanston Street, near the Cathedral 

 [621-7] ; Swanston Street, sewer near Collins Street [615-20, 

 639-43]. Also at Broadhurst's Creek, S.E. of Kilmore, G.S.V. 

 Bb 18 [874]. 



Horizon. — Silurian (Melbournian). 



Chonetes pobusta, sp. nov. (Plate XII., Fig. 8). 



Specific characters. — Shell semi-circular, wider than long. 

 Cardinal extremities obtusely angular, anterior margin well- 

 rounded. Pedicle valve strongly convex with a shallow median 

 fold ; beak slightly projecting. Brachial valve concave, flattened 

 near its cardinal extremities. Shell surface with about 36-40 

 ■well-marked, slightly sinuous and sharply ridged radii, which 

 bifurcate close to the anterior margin. A series of hollow spines 

 (probably eight) attached to the cardinal surface of the ventral 

 valve, and arranged nearly perpendicular to the hinge line. 



Measurements. 

 Length of figured specimen - - 14 mm. 

 Width 20 „ 



Affinities. — This and the species next to be described belong to 

 de Koninck's group of the Striatae. The general shape and sur- 

 face characters of this species in some respects resembles Chonetes 

 minima, Sow. sp.\ a form generally distributed through the 

 Silurian of England and Wales. C. robusta however is altogether 

 a very much larger form, and possesses a distinct median fold. 

 Chonetes acutiradiata, J. Hall, of the Corniferous Limestone 

 (Upper Heldorberg — Devonian), of New York is similar in respect 

 to the radii, but the cardinal extremities are much produced. 

 The original figure of C. acutiradiata'' shows it to difier from our 



1 hoc. supra cit. 



2 Struphoinena acutiradiata, J. Hall, 1843, Nat. Hist. New York, pt. iv.. Geology, p. 171, 

 woodcut 67, No. 3. 



