Miscellanea. 307 



compressed form of the sides (the greatest thickness in Gresslya 

 being always before the beaks, and gradually diminishing towards 

 the posterior end, while the greatest thickness in Notomya is behind 

 the beaks, depriving them of the characteristic wedge-like form of 

 Gresslya,^ The present genus is destitute of the cardinal ridge in 

 the right valve, so remarkable in Gresslya, having in its place a 

 shallow, attenuated, ovate hollow, bounded by two obscure ridges 

 in each valve, thus approaching Pleuromya. The shell also is much 

 thicker than in the above genera, and the impressions of the mus- 

 cular and pallial scars much deeper and more strongly marked in 

 consequence ; the impression of the anterior adductor is pear- 

 shaped, pointed and attenuated above in Gresslya, but simply oval 

 in Notomya. The Plenromyoe. differ in nearly all the same points as 

 Gresslya from the present genus (except the cardinal ridge), and 

 dilFer besides in the elevation or upward curvature of the cardinal 

 line and the convexity of the posterior two-thirds of the ventral 

 margin corresponding with it, those parts being oppositely inclined 

 in Notomya. The oblique mesial or post-m^esial furrow from the 

 beak in the cast oi Notomya does not exist in the other two genera, 

 but in Pleuromya there exists a somewhat similar furrow, but differ- 

 ent in position, arising in froiit of the beaks, and extending directly 

 to the ventral margin close to the anterior end. Cardinia (Ag.), 

 which somewhat resembles the present genus, is distinguished by 

 its entire pallial impression and dental characters. 



Notomya securiformis (M'Coy). PI. XV. figs. 5 & 5 a.j 



Sp. Char. Transversely ovate, flattened ; length two-thirds the 

 width, thickness rather less than half the length ; beaks small, 

 flattened, rather more than one-third the width from the anterior 

 end ; anterior end narrowed, rounded ; posterior end narrow, 

 subtruncate, nearly square; anterior two-thirds of the ventral 

 margin very convex, a shallow concavity in the posterior third ; 

 muscular impressions very large, anterior one deepest, ovate, pos- 

 terior one shallow, broad, reniform ; pallial scar strongly miarked, 

 parallel with the ventral margin as far as the anal angle, then a 

 small subangular sinus before joining the adductor impression; 

 retractor impression small, deep, narrov/, oval; in the cast the 

 oblique furrow from the beak towards the ventral sinus wide, 

 shallow : remains of a cardinal tooth under the beak of the right 

 valve. 

 Length I inch 6 lines, width 2 inches 2 lines, thickness 11 lines. 



The figures of this species display most of the generic characters. 



Sandstone of Wollongong, N. S. Wales. 



Notomya clavata (M'Coy). PL XV. fig. 4. 



Sp. Char. Transversely clavate ; length two-thirds the width, evenly 

 convex, greatest thickness towards the posterior half; beaks very 

 small, compressed, rather more than one-fifth the width from the 

 anterior end ; anterior end very broad, evenly rounded ; anterior 

 third of the ventral margin very convex, middle portion widely 

 concave ; posterior end narrov,'ed, obliquely subtruncate, rounded ; 

 muscular impression shallow, anterior large ovate, posterior broad 

 lunate ; retractor small, broad, oval ; oblique longitudinal furrow 

 from the beak deep, narrow above, widening nearly to the mar- 

 ginal concavity ; impression of one simple cardinal tooth beneath. 



