310 ON LEAIA MITCHELLI. 



Leaia Mitchelli, sp.nov. 



aS^. char. — Carapace valves transversely oblong ; dorsal margin 

 straight, and without any trace of inflection ; anterior outline 

 rather produced and rounded; posterior margin obliquely truncate, 

 slightly em arginate at its junction with the dorsal margin, rounded 

 below and graduating invisibly into the ventral margin; umbones 

 sharp, anterior, but not terminal ; lateral carinse prominent and 

 well marked, increasing in thickness as the umbones are receded 

 from, the anterior slightly curved, but reaching the ventral 

 margins at a point almost vertically beneath the umbones, the 

 posterior straight and diagonal, separating the valves into unequal 

 halves, the anterior being the larger; surface bearing fine, regular, 

 concentric laminae, angulated at the carinse to correspond with the 

 outline of the valves, but frill-like on crossing the former. 



Loc. and Horizon. — Charlestown, between Newcastle and Lake 

 Macquarie : — Upper Coal Measures — Coll. Mitchell. 



