BIVALVIA. 19] 
the recent shell is that in the latter the hinge line appears rather thicker; and the 
same may be said of the Sicilian fossil. 
In this shell the sulci or ridges take their rise, and are most numerous, like the 
two preceding species, on the posterior side, or that on which the ligament is placed, 
where they are somewhat rugose, and descend or curve in an oblique direction over 
the exterior or centre of the shell, and are lost or run out at different distances on the 
ventral margin, most conspicuously so on the anterior portion. These rugosities are 
regular on the posterior side, radiating in an opposite direction, like those upon the 
posterior side of Venus verrucosa, and are probably produced by the lines of growth 
cutting the sculpture at an acute angle; they are most distinct upon the Coralline 
Crag specimens. 
There is a considerable variation in the outline of this species, some individuals 
having a height as great, or greater, than the length, but in general the larger diameter 
is from the anterior to the posterior margin; there is also a difference in the sculpture, 
the lines being much closer or more numerous in some than in others, and they are 
always more distant near the umbo, or on the young shell, and most distinct upon 
the Red Crag specimens. There are the remains of colour in some of my fossils, 
like concentric bands. 
It was at one time thought there was sufficient difference in this species to entitle 
it to more than specific distinction, and it remained in my cabinet under the MS. name 
of Digitaria vulgaris, and perhaps when the animal becomes known, it may present 
characters that are so; but judging from the shell alone, it so strongly resembles some 
of the more aberrant forms of Astarte, that it seems more advisable it should be placed 
here, bearing, as it evidently does, a greater relationship to this genus than either 
to Zellina or Lucina, to which it has been hitherto referred. Unlike the former, it has 
the impression of the mantle entire, or without any inflection, and the impressions of 
the adductors are of an ovate form, the anterior one being rather the longer of the 
two; but unlike the latter, it wants the hgulate or band-shaped impression so charac- 
teristic of that genus. The same obliquity of ridges may be seen upon a small species 
with the hinge of Cardita, a genus probably very closely allied-to the present one. 
19. ASTARTE EXcURRENS, S. Wood. Tab. XVII, fig. 9 ad. 
Spec. Char. Testa minimd, transversd, ovatd, subequilaterali, compressiusculd, striata, 
striis obliquis utrinque excurrentibus; umbonibus depressis, marginibus denticulatis. 
Shell small, transverse, ovate, nearly equilateral, somewhat compressed, covered 
with strize that are not parallel to the margin, but run out from each side; umbones 
depressed ; margins denticulated. 
Largest diameter, 4th of an inch. 
Locality. Cor. Crag, Sutton. 
This shell is not by any means rare at the above locality. It differs from the pre- 
25 
