15 



Notomta Beddomei. (ttov. sp.) 



Shell large, thick, elongate, very convex, inequilateral ; 

 length fully twice the breadth ; beaks gibbose, laxly incurved 

 and approximate, situate at the anterior quarter of the valve ; 

 posterior slope gently arched and greatly produced ; posterior 

 margin slightly compressed ; posterior ridge greatly arched, 

 obtusely angular, abruptly sloping dorsally, and disappearing 

 before reaching the posterior inferior angle ; anterior slope 

 oblique, concave under incurved beaks, and rounded inferiorly ; 

 ventral margin gently curved, obtusely rounded at junction 

 with posterior slope, more acutely rounded at posterior slope ; 

 surface ornamented with a few flattened, distant, concentric 

 folds, which become more dense towards anterior side. 



Length, 1\ inches ; height, 3§ inches ; greatest thickness 

 through centre of both valves, — inches. 



One fine specimen in Tasmanian Museum, collected at 

 Bridgewater Limestone Quarry by Captain Beddome. (Lp. 

 Paselozoic.) The only shell which approaches the above is N. 

 elongata (de Koninck), from which it is easily distinguished by 

 the concave anterior slope, and the absence of a mesial furrow 

 or depression. 



Family Astaetid^. Genus Pachydomits. (Morris.) 

 (Megadesmus.) 



Shell oval, ventricose, very thick ; ligament area external ; 

 lunette more or less distinct ; hinge line sunk ; teeth, one or 

 two, in each valve ; adductor impressions deep ; anterior pedal 

 scar distinct ; pallial line broad and simple, or with a very 

 shallow sinus. (Try on.) 



Paciiydomtjs Kontttcex (srov. sp.) 



Shell transversely oval, solid, thickest at umboes : breadth 

 about three-fourths of the length ; dorsal margin arched ; 

 valves regularly convex ; surface ornamented with numerous, 

 somewhat regular concentric striae ; umboes thick, greatly 

 recurved, and mutually touching each other; some of the 

 specimens attain a large size, and become very thick at the 

 hinge ; there is a single tooth, large and blunted, fits into a 

 corresponding cavity in the hinge of each valve ; the layers of 

 growth on hinge and teeth are very obvious. 



Specimen of moderate size. 



Length, 3| inches ; height. 3 inches ; thickness, 2 inches. 



Very common in tip. Pal. rocks at Cheshunt, St. Paul's 

 River, Boss, Styx Biver, Bridgewater, Ilobart, One Tree 

 Point, Bruny, Maria Island. 



This shell is no doubt identical with the form figured and 

 described as P. glolosus by de Koninck, but quite distinct from 



