40 PLEUKOTOMA. 



G. 4231. Typical adult and senile specimens, and an example 

 in which the lirse are not so bold, and the shell is relatively 

 more tumid. Presented hy John Dennant, Esq. 



G. 4233. Four specimens, in which the ornamentation is much 

 reduced in importance, and numbers of additional spiral lineations 

 are introduced. Presented hy John Pennant, Esq. 



G. 5501. Two specimens, strongly lirate, but more elongate 

 than typical examples. Purchased. 



G. 5499. A smooth specimen, in which the lirse have dis- 

 appeared, or are only represented by obsolete lineations, whilst 

 the growth-lines are more prominent. Purchased. 



Pleurotoma trilirata, sp. nov. 



[Plate III. Figs. l«-rf.] 



Shell small, elongate. Protoconch large, composed of two and 

 a half smooth turns ; the earlier portion is much depressed, and 

 even in the initial part the suture is canaliculate and marginate ; 

 at a later stage the protoconch is longitudinally costate and 

 subnodose at the periphery, and this continues up to the brephic 

 stage, where it gives way to the bold spiral lirse which form the 

 sole ornamentation of the whorls in subsequent stages of growth. 

 Whorls six, flat, suture canaliculate and marginate ; spiral lirae 

 three in number on the penultimate whorl, with a smaller lineation 

 between the posterior two, which becomes more accentuated on 

 the body-whorl. The latter is boldly lirated throughout ; lines of 

 growth inconspicuous. Aperture small, pyriform ; outer margin 

 arcuate ; sinus shallow, situated not far from the suture ; 

 columellar margin smooth, not callous, slightly twisted in front ; 

 anterior canal very short. 



The most interesting feature of this species is the highly 

 sculptured protoconch, which differs from that of any other 

 Australian form here described. The longitudinal costse, how- 

 ever, precede the spiral lirse as in some other species of Pleurotoma. 



Dimensions. — Length 10-5 mm. ; breadth 4 mm.; length of 

 aperture 3-5 mm. 



Form, and Loc. — Eocene : Hobson's Bay, Victoria. 



48052. The type specimen. Purchased. 



I 



