372 Transactions. 



Rhlzothyris elongata n. sp. (Plate XXII, fig. 11 ; Plate XXIII, fig. 11.) 



1905. Bouchardia elongata Park, Trans. N.Z. Inst., vol. 37, p. 541 



{nomen nudum, ascribed to Hutton). 



Three specimens only, of extremely elongate tapering form, have been 

 collected — two by McKay from Hutchinson's Quarry, and one by myself 

 from the dip-slope of the main Mount Brown limestone, Weka Pass. All 

 three are imperfect, and I have selected the least-damaged specimen from 

 Hutchinson's Quarry as the holotype. The hinge -line is broad and little 

 curved, and is nearly the breadth of the shell. The sides taper gradually 

 to a narrow front. The convexity and folding is moderate in all three 



specimens, and the beak little incurved. 



Dimensions in Millimetres. 

 Length. Breadth. Thickness. 

 Holotype .. .. ..55 37 27 



Paratvpe, Hutchinson's Quarry . . 34+ 23-5 10 



Paratype, Weka Pass . . " . . 47 30 19+ 



Rhizothyris curta n. sp. (Plate XXII, fig. 5 ; Plate XXIV, fig. 1.) 



Shell broadly elliptical, with a broad, little-curved hinge-line almost as 

 broad as the shell; sides gently convex and regularly rounded, meeting 

 the nearly straight front in obtuse angles. Valves moderately and nearly 

 equally convex ; anterior commissure nearly straight, with only a very 

 slight, broad, rounded ventral sinuation. Length of holotype, 37 mm. ; 

 breadth, 33 mm.; thickness, 20 mm. 



Type locality : Foot of dip-slope, main Mount Brown limestone, Weka 

 Pass. The species occurs rarely in the type locality and in the uppermost 

 Mount Brown limestone, and one specimen has been obtained from the 

 concretionary bed, Deborah Cutting, Oamaru. It also occurs in a dwarfed 

 form, up to 26 mm. long, in the Maerewhenua greensands. 



Rhizothyris crassa n. sp. (Plate XXIII, figs. 8, 9J 



Shell in outline resembling R. curta. Valves strongly convex, anterior 

 commissure with a broad, fairly deep, ventral sinuation. Beak erect. 

 Length of holotype, 41mm.; breadth, 37-5 mm. ; thickness, 27 mm. 



Type locality : Foot of dip-slope, main Mount Brown limestone, Weka 

 Pass. The 'species in common in the type locality. 



Rhizothyris elliptica n. sp. (Plate XXII, fig. 1 ; Plate XXIII, fig. 3.) 



1915. Rhizothyris rhizoida (Hutt.) Thomson, Trans. N.Z. Inst., 

 vol. 47, p. 398, fig. 5, d (not of Hutton). 



Shell elongate-elliptical, hinge-line broad and little curved, sides lightly 

 convex and regularly rounded, front rounded. Valves moderately convex, 

 anterior commissure with a slight rounded ventral smuation. Length of 

 holotype, 47 mm. ; breadth, 36 mm. ; thickness, 22 mm. 



Type locality : Foot of dip-slope, main Mount Brown limestone, Weka 

 Pass. The species is rare both in the type locality and in the uppermost 

 Mount Brown limestone, and is also found in the Hutchinson's Quarry 

 greensands. Dwarfed forms from 25 mm. to 32 mm. in length are common- 

 in the Maerewhenua greensands. 



