ADDENDA.. 109 



Geological Positions and Localities. This oyster appears to be abundant in the Upper 

 Bathonian Clays of Wiltshire. Mr. Walton has collected it in the Forest Marble of Pound 

 Pili, Farleigh, and liinton, also in the Cornbrash of Ililperton. 



Genus— "-Ilarpax — Parkinson, 1811. Deslongcharaps, 1858. 



Shell irregular, inequivalve, attached by the umbo of the larger or right valve ; surface 

 radiately ribbed or smooth, usually with concentric, irregular, lamellose plications, imbricated 

 or tuberculated ; borders of the valves close fitting and irregular. 



Hinge in the attached valve consisting of a large, flattened, triangular plate, traversed 

 by a central perpendicular or oblique furrow to receive the ligament, with somewhat 

 elevated borders, exterior to which are slightly marked diverging sulcations to receive the 

 elevated borders of the ligamental groove in the other valve ; the outer borders of the 

 plate form lengthened and elevated dental processes. 



Hinge in the left or free valve with a triangular plate traversed mesially by the liga- 

 mental groove, the borders to which are elevated and but slightly diverging ; exterior to 

 these are strongly impressed grooves to receive the dental processes of the other valve ; 

 the dental processes forming the diverging borders of the plate are but little produced. 



The hinge plate in each valve has transverse striations of growth. 



The adductor scar is round, placed posterior to the middle of the valve, and strongly 

 marked ; the pallial sinus is simple. 



The genus Harpax having originally been imperfectly described by Parkinson, and 

 founded upon a single small species, remained but little noticed and accepted by few 

 authors until the year 1858, when it was re-established and amply illustrated in a copious 

 work* on the ' Fossil Plicatulas and allied Genera,' by that eminent and veteran palaeon- 

 tologist M. Eudes, E. Deslongchamps, who to the long list of memoirs in which he has so 

 ably developed and illustrated the Jurassic fossils of Normandy, has added the present, 

 which probably surpasses all the former in the critical acumen and lengthened researches 

 which it has necessitated. Of the fifteen species of Harpax known to M. Deslongchamps 

 all are Liassic, with one exception (//. scajjha), from the ferruginous (Inferior?) Oolite of 

 Longwy ; the following fine species is therefore the first example of the genus in the 

 oolites of this country. 



* Essai sur les Plicatules fossilcs et quelque autre genres voisins on demembres de ces coquilles, 

 par M. J. A. Eudes Deslongcharaps. Extract du Xle volume des ' Memoires de la Societe Liiiueenue Je 

 Normandie,' Caen, 1858. 



