JSIoUusca from the Bol-keveld Beds. 266 



with the shape of Nnculitcs triqueter, Conrad/' but without a 

 clavicular ridge. In shape it is subtrianguiar, broadly ovate, highest 

 anteriorly, nearly as high as long; the surface is moderately convex, 

 most so about the anterior middle of the valve, but the anterior 

 portion in front of and below the beak is suddenly flattened and 

 slightly excavated, producing a marked angulation on the surface 

 along a line descending steeply from the beak to the basal margin, 

 where it is slightly curved forwards. The basal margin is arcuate ; 

 the anterior end is well rounded and abrupt ; the posterior end is 

 subtruncate at the inferior angle and rounded above ; the cardinal 

 line is oblique and straight behind the beak, but in front is sharply 

 bent down nearly at a right angle. The beak is prominent, directed 

 anteriorly, broad, obtuse, rising above the hinge-line, and situated 

 far forward at rather less than one-fourth the length of the shell. 

 The angular ridge on the surface descending from the beak makes 

 an angle of about 75° with the oblique hinge-line iDehind the beak. 

 The hinge-hne shows about 16 transverse teeth. If the internal 

 •clavicular ridge had not been plainly absent, there would have been 

 every reason to compare this form with Nucuutes mjssa, Hall, var. 

 viajora, Clarke,! from the Devonian of the Amazon area, and with 

 A', triqueter, Conrad. 



Dimensions. — Length 14 mm ; height at beak 12 mm. 



Locality. — (No. 96) Gamka Poort. 



BYSSOPTERIA? sp. 



(PI. XXXII., fig. 8.) 



There is one imperfect left valve (No. 82) of a large peetinoid or 

 •aviculoid form which may be referable to the genus Byssopteria, 

 Hall, but its state of preservation does not allow one to decide this 

 point. The shell is triangular, higher than long, alate posteriorly, 

 with the anterior margin nearly vertically truncate the entire height 

 ■of the shell ; the basal and posterior margins form a continuous 

 arc ; the cardinal line is straight. The body of the shell is very 

 weakly convex, and is distinctly marked off by a groove from the 

 flattened triangular posterior wing. The surface of the body and, 

 perhaps, the posterior wing is covered by faint subequal rounded 

 low radiating ribs. 



* Hall, op. cit., p. 326, pi. xlvii., ti<,'s. 17-28. 

 t Clarke, <q). rit., p. 72. pi. viii., fig. 0. 



