158 MOLLUSC A FROM THE CRAG. 



7. CARDIUM PARKINSONL, /. Sowerby. Tab. XIII, fig. 7 a b. 



CARDIUM PARKINSONI. J. Sow. Min. Conch., t. xlix, 1814. 



Woodward. Syn. Table Brit. Foss., p. 43, 1830. 



Id. Geol. of Norf., p. 43, t. ii, fig. 18, 1833. 

 Nyst. Rech. Coq. Foss. Prov. d'Anv., p. 12, No. 48, 1835. 

 Potiez and Mich. Cat. des Moll, de Douai, t. xi, p. 183, 1844. 

 Nyst. Coq. Foss. de Belg., p. 186, pi. xiv, fig. 2 a, b, 1844. 



Spec. Char. Testa magnd, rotundato-ovatd, vel oblique-cordatd, convexd, sub-cequi- 

 laterali ; antice rotundatd, postice sub-angulatd ; costis 28 32 planulatis, sub-imbricatis. 



Shell large, roundedly ovate, or obliquely heart-shaped, convex, sub-equilateral ; 

 anterior side rounded, posterior sub-angulated; ribs 28 32, rather flattened, and 

 slightly imbricated. 



Lengthy 2| inches ; height, 2J inches. 



Localities. Red Crag, Walton-on-the-Naze, Felixstow, Sutton. 

 Mam. Crag? Thorpe (Woodward}. 



This handsome shell appears to be restricted to the Red Crag Period, for the 

 specimens recorded by Woodward were rare or fragmentary, and may have been 

 accidental introductions, as my Norwich collecting friends do not appear to have met 

 with it in their neighbourhood. At Walton-on-the Naze it may be procured in great 

 abundance, and at that rich deposit the specimens are generally in a fine state of pre- 

 servation ; my largest does not exceed the above dimensions, but fragments indicate 

 its having attained a magnitude of at least three inches in diameter. It somewhat 

 resembles in general appearance C. Islandicum, Linn., but differs from that species in 

 the form of its ribs ; it also has a resemblance to C. maculatum, Grael., C. ventricosum, 

 Brug., from the bay of Campeachy, but is never so large, and seldom of such com- 

 parative dimensions, our shell being generally longer than high; it differs from 

 C. edule in being less angulated or pointed, but is of a more quadrate form on the 

 posterior side, although specimens in the young state are exceedingly difficult to be 

 distinguished. The ribs are sometimes rounded, but more generally flattened, and are, 

 in the best preserved specimens, distinctly striated, but I have never been able to 

 count so many as forty, the number given as its specific character in ' Min. Conch.,' 

 and seldom more than thirty-one ; they are often regularly ornamented with dwarf 

 ridges, or sub-imbrications, crossing the prominent parts, and they are more distant than 

 those upon the common cockle, especially on the anterior side of the shell, where, in 

 some specimens, they are often regular and distinctive ; on the posterior side these 

 concentric ridges are coarser and closer together ; the dental characters are prominent, 

 resembling those of edule, though less strongly developed, with a proportionally 

 smaller ligamental area, and the shell is thinner, in all which characters there is a 

 sufficient difference to entitle this to be considered as specifically distinct. 



