290 . Transactions. — Zoology. 



between Ampliidoxa. s.-str. and the subgenus Calymna, Hut- 

 ton, which includes the forms with ribbed whorls. 



Amphidoxa (Calymna) olivacea, n. sp. Plate XXI., figs. 

 13, a, h, 14, 15. 



Shell globosely depressed, perforated, shining, pale yellow- 

 olive, without markings, thin and transparent, with very close- 

 set arcuated ribs, which are flatly rounded, about 10 per mm., 

 interrupted on the surface with several distinct spiral grooves. 

 Spire slightly elevated, obtuse ; apex smooth. Whorls 3, 

 rather rapidly increasing, rounded, the last slightly flattened 

 on the surface, rounded on the base. Suture deep. Aperture 

 oblique, rotundly ovate, slightly excavated by the penultimate 

 whorl. Peristome very thin, straight, regularly arched, 

 the upper part advancing. Columellar margin not re- 

 flected, sharp, vertically slightly arcuated ; outer margin 

 strongly arched, the margins approximating. Umbilicus very 

 narrow, not deep ; umbilical region infundibuliform, faintly 

 striated. 



Diameter, greatest 5mm., least 4mm.; height, 3|-mm. ; 

 aperture, height 2mm., breadth 2^mm. 



Hah. Hillyer's Creek, near Auckland (Ch. T. Musson). 

 Scarce. 



It seems to be rather rare, as amongst the shells collected 

 by Mr. Ch. T. Musson were only three specimens, of which 

 oiily one is in good condition. This one was used for descrip- 

 tion, but I do not think it to be quite adult. Fortunately it 

 contained the dried animal, which I used for preparing jaw 

 and radula. 



Jaw arcuate, rather solid, upper margin straight in the 

 middle ; consisting of numerous vertical plaits, which indent 

 the upper margin. Ends tapering. On the median part of 

 the cutting-edge a well-pronounced projection. The plaits are 

 laid close together, not imbricating. 



Baditla tongue-shaped, consisting of about 100 almost 

 straight transverse rows of teeth, 17 — 8 — 1 — 8 — 17. 



Central rectangular, longer than broad, slightly broader 

 posteriorly ; reflection tricuspid, median cusp long, slender, 

 with a short cutting-point reaching to the posterior eiid of the 

 base. Side-cusps short, rounded, each with a minute cutting- 

 point. 



Laterals symmetrical, the same as the central, but the base 

 slightly rhomboidal, the median cusp somewhat longer, and its 

 cutting-point lying on the following row of teeth. The last 

 two are in transition to marginals. 



Marginals. — The first three with a quadrate base, reflection 

 bicuspid, the inner cusp broad, reaching to the posterior end 

 of the base, and its stout cutting-point over the following row 



