26 Proceedings of the Royal Society of Victoria. 



parallel to the lines of growth, the latter being most noticeable 

 posteriorly, fine radial striations are also just discernible in the 

 neighbourhood of the greatest convexity and on the posterior 

 slope. 



Dimetisiojis. — Antero-posterior diameter, 65 mm.; greatest 

 breadth about 35 mm. from anterior margin, about 30 mm.; 

 thickness through one valve, 16 mm. 



Locality. — Eocene Septarian Limestones, near the Old Cement 

 Works, Balcombe's Bay, Morningtoii. 



Observations. — Only one species of this genus has hitherto 

 been described amongst our fossils, but this by no means fairly 

 represents the actual occurrences. The species at present 

 described is entirely distinct from M. adelaidensis, Tate, from 

 the Adelaide bore. 



Modiola pueblensis, sp. nov. (PL III., Fig. 1). 



Description. — Shell of medium size, oval-oblong, somewhat 

 tumid, with very prominent, tumid, and incurved umbo, which 

 projects forwards little short of the narrow, convexly rounded, 

 anterior margin. Venti'al margin with a slight siims situated in 

 front of the median portion of the shell, the sinus lapidly 

 shallowing out in its ascent to the greatest convexity of the shell. 

 Shell excavated posterior to and anterior to the umbo, the 

 greatest convexity is at about the anterior third, and the greatest 

 breadth a little posterior to the median line. The margin 

 posterior to the umbo is straight, and rapidly ascends to the 

 region of greatest lireadth, thence the descent is con\exly 

 rounded, wedging somewhat posteriorly to join the ventral 

 margin. 



The surface is marked by slightly irregular, close, flat ridges, 

 conforming to the growth of the shell, the grooves between being 

 much nan'ower than the ridges, the growth folds interfering 

 somewhat with the regularity of this sculpture ; the ridges are 

 most luarked anteriorly tending to be less distinct where the 

 convexity of the shell is greatest. 



Dimensions. — Type specimen, antero-posterior diameter, 

 32 mm.; greatest breadth, 17 mm.; breadth at anterior end, 

 about 8 mm.; another specimen, slightly deformed by crushing 



