BIVALVIA. 43 



not, probably, for the organ of attachment, and as in the recent species, their shells 

 vary much in those characters, the secondary fossils were most likely of this genus. 



1. LIMA EXILIS, S. Wood. Tab. VII, fig. 6, ac. 



LIMA EXILIS. S. Wood. Mag. Nat. Hist., New Series, vol. iii, p. 233, Sup., pi. 3, fig. 1, 



1839. 



S. Wood. Catalogue, 1840. 

 Morris. Cat. of Brit. Foss., p. Ill, 1843. 



Spec. Char. Testa ovatd, valde obliqud, depressd, frayili, exili, utroque latere liiante ; 

 costato-striatd, striis 25-35 asperimis, undulatis ; cardinis obliqui area angustd ; auriculis 

 minimis <equalibus. 



Shell ovate, very oblique, somewhat depressed, slender, and fragile, gaping largely 

 on both sides ; striated or costated, striae 25-35, rough, irregular and unequal, 

 cardinal area large, oblique ears, rather small and equal. 



Longitudinal diameter, \\ inch. Height, 1^ inch. 



Locality. Cor. Crag, Ramsholt, Sudbourn. 

 Red Crag, Walton Naze. 



This elegant shell does not appear to have been very scarce in the Coralline 

 Crag Sea, having myself procured a dozen specimens, most of which were from one 

 locality, Ramsholt ; it is also occasionally found in the more tranquilly deposited portion 

 of the Red Crag at Walton Naze, but its fragility in proportion to size is against 

 its preservation in that deposit, as even in the older formation, specimens are not often 

 obtained in a perfect state. 



Messrs. Forbes and Hanley have introduced this fossil into their synonyma of 

 L. hians, considering it only as a variety of that species, to which opinion I am not 

 willing to assent as a marked and striking difference is presented by my fossils 

 sufficient by the ordinary mode of valuation in specific distinction to justify a 

 separation. It somewhat resembles L. inflata, but is flatter and undeserving of that 

 name, and a shell in the British Museum called L. scabretta, approaches it in some 

 respects, but that is also more inflated, and is probably a variety of the injtata ; I 

 have therefore retained it as distinct, being intermediate between the British and 

 Mediterranean species, approaching rather nearer to the latter than to the former. 



It may be more particularly described thus : the form is irregularly ovate, 

 very oblique, gaping on both sides, and covered with raised and slightly undulating 

 costulated striae, these are rough or scabrous, at nearly regular distances, covering 

 in some specimens the entire surface, but generally a small space is left naked 

 on the anterior side ; in L. hians the striae are less regular, thicker on the 

 posterior side, larger and more dissimilar on the anterior, in this they are rather 

 more distant upon the posterior half; the comparative dimensions of this are very 

 different, taking the height at lj inch from the umbo to the ventral margin, the 

 diameter in the opposite direction is equal to 1 \ inch, but in hians the height is at 



