178 



Dimensions. — Antero- posterior diameter, 18 ; umbo- ventral 

 diameter, 9 ; sectional diameter of one valve, 3'5 millimetres. 



Locality. — Lower beds at Muddy Creek. 



This species is similar to N". rostrata, Spengler, and J¥. Angasi, 

 E. A. Smith, but it has a shorter anterior side. 



Young ? fig. 2b, which seems indistinguishable from JV. inflata, 

 Jeffreys, P.Z.S., 1881, t. 71, f. 8, has the following dimensions : 

 — Antero-posterior diameter, 6'5 ; umbo-ventral diameter, 4*5 

 millimetres. 



Nesera Adelaidensis, spec. nov. Plate xix., fig. 8. 



Ovate, rather depressed, inequilateral, anterior end rounded, 

 posteriorly produced into a longish slender beak ; the beak is 

 obliquely bisected by a sharp radiating ridge. 



The surface is ornamented by few, regular, distant, short, 

 and thin lamellae. Interior unknown. 



Dimensions. — Antero-posterior diameter, 5 ; umbo-ventral 

 diameter, 3 ; sectional diameter of closed valves, 1*5 milli- 

 metres. 



Locality. — Adelaide bore. 



Nesera (Rhinomya) latesulcata, spec. nov. Plate xix., fig. 7. 



Broadly-triangular, inequilateral, thin, flat, rounded an- 

 teriorly, produced and subrostrated posteriorly; ventral 

 margin very slightly arched medially, inconspicuously in- 

 sinuated posteriorly, somewhat rapidly ascending anteriorly ; 

 post-dorsal margin straight, much longer than the slightly 

 arched front-dorsal margin ; the posterior margin is very 

 narrow, straight, and forming an obtuse angle with the ventral 

 margin. The umbonal region is finely concentrically striated, 

 and surmounted by a smooth umbonal papilla ; the rest of the 

 surface ornamented with six acute concentric folds, raised into 

 thin, short, erect lamellae ; the broad interspaces finely concen- 

 trically striated. The post-dorsal area is defined by a raised 

 line proceeding from the post-ventral angle towards the umbo 

 as far as the smooth umbonal area. The right valve has a 

 short anterior tooth, and an elongate lamellar tooth posteriorly 

 for about one-third the distance from the umbo, beyond which 

 it is continued as a shelf-like process to the extremity of the 

 post-dorsal margin. There is no cartilage-process. 



Dimensions. — Antero-posterior diameter, 4 ; umbo-ventral 

 diameter, 25 millimetres. 



Locality. — Adelaide bore. 



FAMILY SAXICAVIDJE. 

 Saxicava arctica, Linn. 

 Synonym. — Saxicava australis (Lamk.), Tate in Trans. Roy. 

 Soc, S. Aust., for 1865, pi. xii., fig. 8. 



