BIVALVIA. 157 



6. CARDIUM ANGUSTATUM, /. Sowerby. Tab. XIII, fig, 6 a c. 



CARDIUM ANGUSTATUM. J. Sow. Min. Conch, t. 283, fig. 2, 1821. 

 Woodward. Syn. Tab., p. 13, 1830. 

 S. Wood. Catalogue, 1840. 



$pec. Char. Testa transversd, elongato-ovatd, parum incequilaterali ; depressiusculd, 

 tenui ; antice rotundatd, inflatd; postice attenuatd, compressiusculd ; costis 27 32 depressis, 

 planulatis, approximatis, aspens ; margine ventrali recto vel coarctato. 



Shell transverse, elongato-ovate, slightly inequilateral, somewhat depressed, 

 thin ; anterior side rounded, and inflated, posterior attenuated, and compressed ; 

 ribs 27 32, depressed, flattened, approximating, roughened ; ventral margin 

 straight, or rather contracted. 



Length, \\ inch; height, 1 inch. 



Localities. Red Crag, Sutton, Bawdsey, Ramsholt, Alderton. 



This species is very abundant in one or two localities, and it does not appear to 

 have been as yet met with in any other part of the World than in the Red Crag. 



In Min. Conch.' above referred to, vol. iii, p. 149, it is stated to be abundant in 

 the Crag of Norfolk, but it is not enumerated amongst the shells from near Norwich by 

 Woodward, nor have I seen a specimen from that Formation. This species may be well 

 determined, although occasionally it presents some difference in outward form, but the 

 posterior side is always more or less attenuated, and the dorsal margin on that side 

 slopes at a considerable angle from the umbo ; the line of the ventral margin, also, in 

 that half of the shell, is contracted or drawn inwards, giving it a pointed form, 

 considerably more so than in any variety of the common cockle, from which it also 

 differs in having a greater number of ribs, and these are flatter. The umbo is nearly 

 equidistant from each extremity, but the posterior side is much the smaller ; the marks 

 of the ribs are very distinct halfway into the interior, and in some very thin specimens 

 they may be seen up to the umbo. Externally they are flat, broad, and striated, with 

 a narrow space between them ; they are more distinct on the anterior side and body 

 of the shell, as in C. edule, becoming obsolete on the posterior slope, and where the 

 exterior is well preserved, they show a sub -imbricated surface all over. In a part of 

 the cliff by the river side at Ramsholt, I have found this species in situ with the valves 

 united, where they show a very slight gape on the posterior side ; the specimens are 

 particularly thin and tender, with generally a loss of a considerable part of the exterior ; 

 in these specimens the ligament is well preserved. 



