46 PLEUBOTOMA. 



Dimensions. — Length 18 mm. ; breadth 7-5 mm. ; length of 

 aperture 10mm. 



Form, and Loc. — Miocene : New Zealand. 



G. 9498. Several specimens, from Parimoa, Middle Island. 



W. B. D. Mantell Coll. 



G. 9495. A tumid variety, from Awamoa. Sir James Hector Coll. 



Pleurotoma •wanganuiensis, Hutton. 



1873. Pleurotoma wanganuiensis, Hutton, Cat. Tert. Moll. N.Z. p. 4. 

 1893. Pleurotoma wanganuiensis, Hutton, Linn. See. N.S.W., Macleay 

 Mem. Vol. p. 50, pi. vi. fig. 28. 



Professor Hutton describes this as follows: — "Shell fusiform, 

 the spire longer than the body-whorl. Whorls strongly spirally 

 ribbed, and obliquely longitudinally ribbed in the centre. From 

 13 to 16 longitudinal ribs in a whorl. Suture very finely obliquely 

 striated, and with a spiral rib. Aperture oval, canal short and 

 recurved." 



Specimens in the British Museum agree very well with this 

 description, but the figure given in the memoir above cited 

 represents a more tumid variety. The protoconch (Plate II. 

 Pigs. Wa-h) is most remarkable, and merits detailed description. 

 Of the four specimens in the collection, two exhibit the 

 characteristic fracture or undulation at the termination of growth 

 of the protoconch. As thus defined, the latter is composed of 

 from two and a half to three turns; the initial turn is smooth 

 and obsoletely striated, and this is followed by an obtuse angulation 

 which rapidly develops into a bold, acute, median spiral carina, 

 with a conspicuous lineation both above and below it, and another 

 bordering the suture. Up to this point, no longitudinal costse or 

 other ornamentation are developed, and if the growth had con- 

 tinued in the same manner a shell somewhat resembling P. alia 

 would have resulted. Instead of that, however, the brephic stage 

 is characterized from its commencement by the profuse ornamen- 

 tation, suddenly introduced, which obtains in the adult. This 

 should prove of material value in working out the genetic relation- 

 ships of the group. 



