DESCRIPTION OF SHELLS. 169 
they in general occupy every alternate rib ; but sometimes one rib will be missed, 
and then there are three ribs together without scales. 
Cardium ordinatum. (Tab. III. fig. 17.) 
Spec. Cuar.—Suborbicular, convex, posteriorly obliquely truncated, orna- 
mented with numerous rounded cost, which are regularly covered by thick 
lunate scales. 
The cost on this neat shell are about thirty-six in number ; they increase 
slightly in size towards the posterior extremity, and are largest and widest apart 
upon the boundary of the posterior area. The thick scales or granules are very 
numerous and regular. 
Found with the last at Bracklesham Bay by Mr. Edwards. 
Cardita planicosta. (Tab. II. fig. 14.) 
The shell here figured has the furrows very deep and the ribs square, and 
maintains that character in some individuals which are so large that they can 
hardly be thought to be the same species as that shown at fig. 18, which has the 
furrows shallow and the edges of the ribs rounded ; but upon examination it will 
be found that near the beaks, the furrows are like those in fig. 14; and the 
distance from the beak where they become shallow is so various in different 
individuals, that it must be admitted that one is only a younger shell than the 
other of the same species. 
Cardita elegans. (Tab. III. fig. 15.) 
This shell is found in light-coloured sand, and generally in such a decayed 
state, that it is doubtful whether it be rightly named. 
Byssoarca Branderi. (Tab. Il. fig. 23.) 
Arca Branderi of ‘ Mineral Conchology’ appearing to be a young shell of A. 
aantula of Deshayes rather than A. biangula, Deshayes, it is thought necessary 
to retain that name for the A. hiantula. The Bracklesham specimens are as large 
as the French ones, and even larger. This species differs from A. biangula, 
Deshayes, in having a much less acute keel. 
