Vol.51.] MR. R. B. NEWTON ON FOSSILS FK05I MADAGASCAR. 81 



oblique, and extending nearly -| the height of the shell ; umbones 

 obtuse and terminating on the dorso- anterior margin of the hinge- 

 line ; anterior wing rudimentary, posterior oblique ; surface worn, 

 but showing concentric foldings at the margins of the valves. 



Dimensions : specimen with valves in contact. — Height = 45 mm. ; 

 length=30 mm. ; diameter = 25 inm. 



The ligamental space between the hinges is wide and deep, but 

 through bad preservation none of the pits are visible. This form 

 differs from G. (Gastrochama) tortuosa, J. de G. Sowerby, 1 in being 

 much more convex, less tortuous, longer, and in possessing a deeper 

 ligamental furrow. It is distinguished from G. Hartmanni, 

 Minister, 2 by its rudimentary anterior auricle and shorter hinge. 



Horizon. — Lower Oolite. 



Loc. — About 3 miles north of Iraony. 



Lima iraonensis, sp. nov. (PI. III. fig, 2.) 



Shell subtriangular, rather flattened, having its greatest convexity 

 over the umbonal and posterior areas, and more or less compressed 

 in the anterior and ventral directions ; umbo acute and incurved ; 

 anterior auricle short and sloping ; posterior area obliquely margined, 

 and making a vertical descent to the elongate and concave byssal 

 region; surface ornamented with numerous smooth and flattened 

 ribs (about 54) radiating from the umbo ; these ribs attain their 

 maximum width near the ventral margin, where they measure 1mm. 

 across ; they take a slightly undulating course, and are separated 

 by well defined grooves minutely punctated ; concentric lines of 

 growth cross the ribs at irregular intervals ; the byssal area is 

 marked with coarse concave costse ; ventral margin imperfect. 



Dimensions. — Height = 35 mm.; length = 37 mm. ; depth 

 = 10 mm. (max.). 



This specimen is more acutely umboned than Lima impressa of 

 Morris & Lycett, and its posterior margin is much sharper ; both, 

 however, have the punctations between the ribs. It approximates 

 rather closely to L. amnifera of Whidborne, 3 from the Inferior Oolite, 

 but the ribs in this form appear to stop short over the umbonal area, 

 and the punctae are not so numerous. It is named Lima iraonensis 

 after its locality. 



Horizon. — Lower Oolite. 



Loc. — About 3 miles north of Iraony. 



PxEROPERNA (allied to) COSTATtTLA, (PI. III. fig. 1.) 



This is represented by the impression of a left valve of a very 

 young specimen contained in the same sandstone as that in which 

 specimens of Trigonia pullus, etc. occur. It is well, ornamented 

 with curved radiating ribs, and the extent of the hinge-line is 

 moderately definite, but the groove on the posterior expansion is 

 not clearly seen. 



1 ' Mineral Conchology,' vol. vi. (1826) p. 49, pi. dxsvi. fig. 1. 



2 Golclt'uss, ' Petref. Germanise,' vol. ii. (1836) p. 122, pi. cxv. fig. 7. 



3 Quart. Journ. Greol. Soc. vol. xxxix. (1883) p. 501, pi. xvii. fig. 2. 

 Q. J. G. B. No. 201. a 



