490 THE LAND AND FRESH-WATER MOLLUSCA OF NEW ZEALAND, 



Radula (fig. 4c?) tongue-shaped, transverse rows straight, con- 

 sisting of 18 — 1 — 18 teeth, of which 3 to 4 may be considered as 

 laterals. Central tooth small, base longer than broad, nariow 

 and rounded anteriorly, broader and almost straight on the 

 posterior end. Reflection small, rounded, with one sharp median 

 cutting point, extending very little beyond the middle of the base. 

 Lateral teeth broader, quadrate, reflection broad, short, bicuspid, 

 with one short cutting point on each cusp, not reaching the 

 posterior margin of the base. 



There follow a few transition teeth, going over from bicuspid to 

 tri- and quadricuspid marginals, which are much broader than 

 long, the cutting points rather long and sharp. The second 

 cutting point is the longest. Last marginal with three cutting 

 points only. 



Therasia Traversi, E. A. Smith, sp. 

 (PI. xxiL figs, b-ba.) 



This shell was classed by its author under Thalassia, but on 

 examining the radula of the animal I at once saw that it really 

 belongs to the section Therasia, Hutton. As first pointed out by 

 Prof. F. W. Hutton, the shells in both sections, Thalassohelix and 

 Therasia, show almost the same characters, and it is therefore 

 necessary to examine the radula for ascertaining the respective 

 section. The dentition of :Z^. Traversi having never been examined 

 before, I propose to give description and figures of it. 



Jaw (fig. 5) slightly arcuate, membranaceous, the ends bent 

 upwards. It is composed of numerous narrow nearly vertical 

 plaits, partly overlying each other, broadly indenting the upper 

 margin. 



Radula (fig. 5a) tongue-shaped, the straight transverse rows 

 consisting of 34 — 1 — 34 teeth, of which 14 are laterals. Central 

 tooth quadrangular, somewhat longer than broad, with a tri- 

 angular reflection, bearing one short median cutting point, which 

 does not extend to the posterior end of the base. Laterals 

 slightly broader, bicuspid, the inner cusp much broader and 

 longer than the anterior one, each of them being provided with a 



