Pdhmmtologii of the Older Tertiary. 327 



convex and furnished medially with two spiral lirae which mark 

 exactly the position of the sinus ; a third spiral thread is 

 usually visible just above the anterior suture, and a fourth 

 weak one just below the posterior suture on the earlier spire 

 whorls, while a fifth makes its appearance on the penultimate 

 and antepenultimate whorls and the posterior sutural thread 

 becomes stronger ; on the body-whorl below the sinus threads 

 there are eight or nine stronger spiral lirae, and the space 

 between the suture and the keel is strongly concave. The whole 

 shell surface is finely spirally striate, the striae tending to be 

 slightly undulatory owing to irregularities of QTOwth, and in- 

 creasing in strength towards the anterior of the shell. The 

 spiral sculpture is crossed transversely by sinuated gTowth lines 

 and striae of unequal 'strength. Sinus broad and deep, and dis- 

 tinctly margined by the lirae forming the keel. Aperture large, 

 pyriform, and extending- to a short, broad, open, slightly bent 

 canal ; outer lip thin and strongly arched at the middle, 

 crenulate internally in conformity with the stronger spiral 

 threads ; columella margin smooth and slightly enamelled. 



Dimensions. — -Length, 3(S nmi. ; breadth of body-whorl, 17 

 mm. ; leng-th of aperture, 19 mm. ; breadth of aperture, 7 

 mm. ; breadth of canal, 3 mm. ; length of canal, about 5 

 mm. Smaller specimens range — length 28, breadth 14, 27 by 

 13, and 25 by 12.5. 



Locality. — Lower beds of Muddy Creek, near Hamilton, 

 Western Victoria ; clays of the Old Cement Works, Balcombe's 

 Bay, Mornington. — Balcombian. — Eocene. 



Observations. — The placing of this species in Pleurotoma 

 might at first sight be questioned, but it agrees more closely 

 with this genus than any other ; its characters place it in the 

 same group as Pleurotoma septemlirata, Harris, which originally 

 had the manuscript name of Pleurotoma perarata by Professor 

 Tate, and is quoted under that name by Monsieur M. Cossman 

 in his Essais de Paleoconchologie Comparee Deux. Liv., p. 77, 

 where he speaks of it as an aberrant form of this genus. 



The present species differs from P. septemlirata, Harris, in 

 general habit being a relatively broader form, with a shorter 

 and more rapidly tapering spire, a longer aperture, shorter and 

 broader canal, broader sinus, and finer sculpture. It is also 



