158 EOCENE MOLLUSC A. 



would rather imply that it is a tender shell; but this does not appear to be so with 

 Mr. Edwards's specimens. 



It is well known that beds of four different ages occur in the Cliff near Heme Bay ; 

 but all the specimens of this species that I have seen appear to have come from the 

 Thanet Sands, 



Eig. 8, Tab. XXIV, represents a specimen from a well at Hampstead, which probably 

 belongs to this species. It is rather more ridged than the Heme Bay specimens, and it 

 has a more elevated umbo. I have given to it the provisional name of A. tenera var. 

 Hampsteadiensis . 



5. AsTARTE ? MODICELLA, 8. Wood. Tab. XXI, fig. 2 a, h. 



Spec. Char. A. Testa minima, ovato-suhtrigond, compressiusculd, lavigatd, valde incB- 

 qidlaterali ; latere postico hrevissimo, obtuso, subfruncafo, antico producto, oltuso ; umho- 

 nibus minimis ; cardine brevi, unidentato, dentibus lateralibus nullis ; margine integro. 



Shell small, ovately triangular, somewhat depressed, smooth externally, very inequi- 

 lateral ; pedal side large and obtuse ; umbo small ; hinge of right valve with one denticle ; 

 margins smooth. 



Diameter, y^th of an inch. 



Locality. Stubbington [Edwards). 



A single valve, as represented, is in Mr. Edwards's cabinet. It is a right valve, with 

 its dentition somewhat like that of Astarte in having only one triangular and slightly 

 diverging cardinal tooth ; but it has no lateral denticle on the pedal side. In my 

 Monograph of the Crag Mollusca are introduced several species of small bivalves, which 

 accord with the diagnosis of Astarte, one of which {triangularis) was made the type of 

 a new genus (as is well known) under the name Goodallia by Turton, who erroneously 

 considered it as having an internal connector ; and it was called Mactra by his predecessor 

 Montagu ; but it possesses all the characters of Astarte. 



There are some bivalves belonging to the Eocene Period which have been figured and 

 described by M. Deshayes under the generic name of Goodallia (' Desc. des An. sans 

 vert, du Bas. de Par.,' t. i, pp. 783 — 786, pi. 63). These resemble in outward form and 

 magnitude the small species of Crag bivalves to which I have referred ; but they appear 

 to exhibit a difference in the dental furniture, reversing as it were the formula of the 

 genus Astarte ; the right valve having two diverging teeth or denticles with a triangular 

 cavity between them, into which a large triangular tooth is inserted from the left valve 

 (that is, according to the representations), contrary to what it is in Astarte, where the large 

 triangular tooth is in the right valve, and the two diverging teeth in the left. It is 

 expressly stated in the diagnosis of Goodallia by Deshayes, that the margins are in- 

 variably smooth. " Les bords sont simple sans aucune trace de dentaluresj" p. 782. 



