BIVALVIA. 155 



lated edge of the shell as probably analogous to the outer lip of some univalves, where 

 the margin of the aperture is denticulated only in the adult state. 



This genus does not appear to be present in the Eocene Formations of France ; in 

 our own country, I know it only from that portion of the Lower Tertiaries which is 

 inferior to the Bagshot Sands, with the somewhat doubtful exception of the shell figured 

 as Astarte modicella. 



The Crag shells of this genus, though of thick and solid texture, are frequently 

 perforated by some of the zoophagous feeders, but they seldom show any erosion at the 

 umbones. Both these actions appear pecuhar to some deposits only. Some of the older 

 Tertiary specimens are much eroded at the umbones, while others of the same species 

 from another locality are not at all so. 



1. Astarte Clarendonensis, Edwards MS. Tab. XXIV, fig. 11 a, b. 



Spec. Char. Testa magna, crassissimd, irregidariter quadrangidatd, tumidiusculd, 

 sublisvigatd, valde incequilaterali ; pedi-regione brevissimd, subtruncatd, altera longiore, 

 subqiiadratd, compressiusculd ; impressionibus muscularibus proftmdis ; marginibus crenu- 

 latis. 



Shell large, very thick and strong, irregularly quadrangular, slightly tumid, and 

 nearly smooth ; very inequilateral ; umbones depressed, very excentric ; pedal region 

 short, anal side truncated, and somewhat compressed ; muscular impressions deep ; 

 margins crenulated. 



Length, If inch ; height, \\ inch. 



Locality. London Clay : Clarendon. 



This species has yielded to Mr. Edwards a great number of specimens, but I do not 

 see among them a very young individual, although one has its margin smooth, and as 

 such I presume it is not full grown. The surface where perfect appears to have been 

 nearly smooth, showing only very fine lines of growth. The umbones of all the speci- 

 mens have been eroded, and I am unable to see if the very young state of the shell was 

 covered with ridges. The shell has a tolerably large lunule not very strongly defined, 

 but this varies according to the tumidity of the individual specimen. The proportional 

 dimensions show considerable variation. 



