29G Transactions. — Zoology. 



Radiila long and narrow, consisting of about 100 straight 

 transverse rows of teeth, 7—4 — 1 — 4^ — 7. 



Central tooth rectangular, considerably longer than broad, 

 reflection tricuspid, median cusp slender, half the length 

 of the base, with a short blunt cutting-point ; side-cusps 

 small, rounded, each with one rudimentary cutting-point. 



The first two laterals with the base like the central, tri- 

 cusjDid, median cusp long and slender, reaching with its very 

 short cutting-point to the posterior end of the base ; side-cusps 

 sinuated, one very short cutting-point on each. In the third 

 and fourth the reflection is larger, the median cusp shorter, 

 its cutting-point longer and passing a little over the next row 

 of teeth ; the inner side-cusp obliterates, and there is a rather 

 long cutting-point ; the outer side-cusp is rounded, and sup- 

 ports a minute cutting-point only. 



Marginals. — The first two with the reflected margin as 

 broad as long, in shape like the last lateral ; median cutting- 

 point stout and rather long, the side cutting-points as in the 

 last lateral. The following marginals get much broader than 

 long, tridentate, the last two without visible denticulation. 



Thera stipulata, Eeeve. From Owaka (Clutha), South Island. 



Plate XXII., figs. 34, 35. 



The dentition of this mollusc has already been described 

 by Professor F. W. Hutton in Trans. N.Z. Inst., vol. xvi. 

 The dentition of several specimens which I examined showed 

 a great variability in the number of laterals, and especially in 

 the form of the last marginals. Professor Hutton gives the 

 number of teeth 12 — 1 — 12, of which three or four are laterals. 

 In one specimen I found the dentition to be 10 — 4 — 1 — 4 — 10, 

 and this one is figured. The twelfth tooth has four denticles, 

 and the last three. In another specimen the dentition was 

 10 — 6 — 1 — 6 — 10, the last two marginals, which are figured, 

 differing considerably from those on the other radula. 



Thera barbatula, Eeeve (=H. beta, Pf.). From Dunediu. 

 Plate XXII. , figs. 36, 37. 



Jaiv almost straight, convex on the upper margin, straight 

 on the cutting-margin, but with a faint indication of a median 

 projection ; very thin, fragile, and transparent ; broadly and 

 faintly vertically striated, the cutting-margin slightly and 

 broadly denticulated. Sometimes a transverse line crosses 

 the vertical strite in the middle. 



Radula tongue-shaped, formed by about 100 almost straight 

 transverse rows of teeth, 15 — 1 — 15, of which six or seven 

 may be taken as laterals. 



Central tooth rectangular, longer than broad, reflection 

 tricuspid, median cusp reaching to the middle of the base, and 



