PLEtTKOTOMA. 45 



anteriorly; outermargin thin, undulating; sinus broad and shallow; 

 columella covered by a thin deposit of vertically striated callus, 

 twisted anteriorly ; canal long, curved, broad in front. 



This shell agrees with others here described in being longi- 

 tudinally costated in the earlier stages of growth, which costse 

 disappear in the adult. It has the aspect of what is generally 

 included under Surcula, but the sinus is far removed from the 

 suture, as in typical Pleiirotoma. 



Dimensions. — Length 16'5mm. ; breadth 6 mm.; length of 

 aperture 9 5 mm. 



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



48052. The type specimen. Purchased. 



Pleurotoma alta, nom. mut. 



1873. Pleurotoma pagoda, Hutton, Cat. Tert. Moll. N.Z. p. 5 {non Reeve). 

 1893. Pleurotoma pagoda, Hutton, Linn. Soc. N.S.W., Macleay Mem. Vol. 



p. 48, pi. vi. fig. 21. 



Protoconch composed of two elevated smooth turns ; whorls 

 six in number, smooth, or only marked with growth-lines, very 

 strongly and acutely keeled at the periphery, and with one or 

 two inconspicuous spiral lineations, as an individual characteristic, 

 above or below the keel ; body- whorl subangulate in front, denoting 

 the position of growth as the suture became developed ; aperture 

 ovate, contracted anteriorly, and terminating in a rather long canal; 

 sinus deep, situated between the keel and the suture, but nearer 

 the former ; columella twisted, covered with a smooth, thin deposit 

 of shelly enamel. 



On conchological grounds this species might be relegated to 

 Surcula, but, as previously remarked, any such reference must 

 always be exceedingly doubtful with fossil specimens. An 

 interesting point is that, whilst many strongly keeled species 

 of PLEUEOTOMiii.a; bear traces of angulation in the protoconch 

 which lead up to the keel in subsequent stages of growth, 

 P. alta is without this in spite of the fact that the carina is 

 most strongly developed in the brephic stage. This species has 

 considerable analogy with Surctila jani, Bellardi, from the Upper 

 Miocene of the Piedmont basin. The specific name alta is here 

 proposed in substitution for pngoda, preoccupied, as iudicatud. 



