Tno'siiiO'S .—Geplogy of Middle Waipara and Weka Pass Districf . 373 



Rhizothyris fortis n. sp. (Plate XXIII, figs. 1, 2.) 



Shell elongate-elliptical, hinge-line fairly bread and little curved, sides 

 lightly convex, rounded, front narrowly truncate and nearly straight. 

 Valves strongly convex, anterior commissure with a broad ventral sinu- 

 ation. Beak nearly erect. Length of holotype, 60 mm. ; breadth, 44*5 mm. ; 

 thickness, 36 mm. 



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

 Pass. Two specimens only referable to this species have been found in 

 the type locality, and two in the uppermost Mount Brown limestone. 



Rhizothyris obesa n. sp. (Plate XXIII, figs. 6, 10.) 



The outline resembles that of R. scutum, but the hinge-line is slightly 

 more curved, and there is a greater approach to an elliptical shape. The 

 valves are markedly convex, a character which differentiates the species 

 from both R. scutum and R. elliptica, and the shell is also more folded and 

 the beak more incurved than in these species. Apparently corresponding 

 to the incurvature of the beak, the foramen is slightly remigrant with 

 an indication of pseudotela. Length of holotype, 48-5 mm. ; breadth, 

 39 mm.; thickness, 28-5 mm. 



Type locality : Foot of dip-slope, main Mount Brown limestone (D), 

 Weka Pass. A single specimen was obtained from the uppermost Mount 

 Brown beds, in the Neothyris shell-bed of Weka Pass Stream. 



Rhizothyris lateralis n. sp. (Plate XXII, fig. 8; Plate XXIV, fig. 4.) 



Shell subcircular, hinge-line broad but slightly curved, sides convex 

 and rounded, beak-margins nearly straight, front rounded. Valves 

 moderately convex ; there is a broad rounded sinuation in the anterior 

 commissure. Length of holotype, 38 mm. ; breadth, 37 mm. ; thickness, 

 20 mm. 



Type locality : Mount Brown beds, Weka Pass. It is uncertain whether 

 the specimen came from the main limestone or the uppermost limestone. 

 No examples are known from other localities. 



Rhizothyris pirum n. sp. (Plate XXII, fig. 9; Plate XXIII, fig. 5.) 



Shell broadly ovate or pear-shaped, with a moderately broad and curved 

 hinge-line, sides convex and rounded, front truncated and gently rounded. 

 Valves moderately convex, anterior sinuation slight. Length of holotype, 

 34 mm.; breadth, 28 mm.; thickness, 18 mm. 



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

 Pass. There is only one other specimen referable to the species, from 

 the escarpment of the same beds, overlooking the Weka Pass. 



Rhizothyris ovata n. sp. (Plate XXII, fig. 7 ; Plate XXIV, fig. 6.) 



Shell ov^ate, with a moderately broad, curved hinge-line, sides lightly 

 convex and rounded, front truncate and gently rounded. The valves are 

 moderately convex, anterior sinuation slight. Length of holotype, 36 mm. ; 

 breadth, 28 mm. ; thickness, 18 mm. 



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

 Pass. The species is also known from the greensands of Target Gully 

 and Hutchinson's Quarry, Oamaru, and by a single specimen from the 

 Maerewhenua greensands. The majority of the specimens from the latter 

 locality belong to a similar ovate species, but with a shorter beak. 



