140 



as far as the scars of the central muscles, which are in the posterior third of 

 the valve, are oval in form, and are about as far apart as half of the width 

 of the cardinal line. A short distance in advance of these scars, but in 

 the anterior half of the valve are the prints of the two anterior lat- 

 erals; these are round, unusually large and are as far apart as the 

 central muscles. At about equal distance from these four muscle scars 

 and at the centre of the valve is a small pit, with a still smaller one in 

 front of it, whose function is unknown. A short mesian ridge extends 

 forward from between the scars of the anterior " j " laterals to two diverg- 

 ing furrows in front of these ; these run from the point of divergence half 

 way to the margins of the valve. In front of the forks of these furrows 

 is a shallow round area, which with the space between the forked groove, 

 is raised on the inside of the valve. Two strong ridges more widely sepa- 

 rated at the back than those of the ventral valve, and less divergent, 

 spread from the umbo. Outside of these diverging ridges are the prints 

 o* the posterior laterals. Running forward from the ridges in a curve 

 parallel to the margin of the valve, vascular grooves are faintly indicated, 

 and still more indistinct are traces of the interior branches of these 

 trunks. 



Sculpture. At the umbo the dorsal valve is granulated, but concentric 

 stride appear at one millimetre from the umbo, and farther out the surface 

 of the valve is diversified with numerous concentric ridges, to which the 

 roughened surface of the shell give a granulated crest. The ventral valve 

 is similarly marked, but there are concentric growth furrows at intervals. 



Size. The ventral valve has a length of 12 mm. and a width of 11 mm. 

 In the dorsal the length and width are each 11 mm. 



Horizon and locality. In the sandstones and sandy shales of Assise 

 E. 2 (a 1 ?), at Youngs point, near George river station, N.S. 



The approximated central muscles and large widespread scars of the 

 anterior laterals of the dorsal valve in this species distinguish it from all 

 other Oboli, and from this and the peculiar grouping of the central group 

 of muscles, the trivial name is derived. 



i 

 PAL^OBOLUS, sub-genus. 



" Distinguished from Obolus proper by the close approximation of the 



Palseobolus vascular trunks, as shown by their impression on the ventral valve, and 



how known, ^y. j. ne f orwar( j direction of its branches. The callus of the visceral cavity 



of this valve is correspondingly narrow (therefore the muscle scars are 



also approximated). Yet the valve is round as in Obolus." [Bull. Nat. 



Hist. Soc. KB., Vo'. IV., p. 202.] 



