44 PLEUEOTOMA. 



a single, somewhat distant series of coarse, blunt, somewhat square 

 tubercles. These are exactly oa the line of the sinus, and at each 

 side the lines of growth curve away from it. The sinus itself 

 is deep, broad, and somewhat quadrate. The aperture is long and 

 round, rather square posteriorly, and the canal is long and only 

 slightly curved." 



The marginate character of the protoconch is noteworthy ; from 

 its metamorphosis in later stages of growth, it would appear that 

 the species has descended from a stock in which the suture was 

 accompanied by a large flat keel, though no shell of that character 

 has been recorded as occurring in the Australian Tertiaries. 



Another point of interest in this species is its compound character : 

 it possesses the tubercular sutural coronation and produced spire 

 characteristic of Clavatula, and shows what value is to be placed 

 on that feature ; the special nature of the peripheral carina and 

 the arcuate, long canal somewhat resemble Surcula; whilst the 

 position of the suture and other general features of the shell 

 recall Pleurotoma. Clearly it was pregnant with evolutionary 

 possibilities. 



Dimensions. — Length 12 mm. ; breadth 4 mm. ; length of 

 aperture 7 mm. 



Form, and Loc. — Eocene : Muddy Creek, Victoria. 



G. 9329. Three specimens. Purchased. 



Pleurotoma optata, sp. nov. 



[Plate III. Figs. 4«-A.] 



Shell fusiform ; aperture (with anterior canal) more than one- 

 half the length of the whole shell ; whorls seven in number, 

 slightly convex, keeled above and below the suture, which is 

 near the centre of the whorls, the anterior keel being the most 

 prominent ; the other ornament consists of several closely-set 

 small spiral lineations, crossed by rather conspicuous growth-lines, 

 and accompanied by a peculiar damascened structure. Protoconch 

 composed of two smooth turns, the anterior being subangulate 

 and vertically striated ; terminating abruptly against the shell of 

 the brephic stage, which is longitudinally, obliquely costated 

 and marginate. Aperture elongately pyriform, much constricted 



i 



