Mr. T. Davidson on the genus Waltonia. 475 
a strong elevated central plate arises near the umbo, describing a 
gentle curve, diverging more obliquely again, and by another 
curve attains the central ridge of the dorsal valve on which it 
rests, and from whence it descends, forming a gentle diagonal 
line to the bottom of the ventral valve. From the inner edge 
of both the dental sockets of this valve a ribbon-shaped lamella 
by a gentle curve rises to near the middle of the central plate to 
which they are attached. 
Obs. From the inspection of this shell it will be seen, that 
by its beak, foramen and teeth it differs considerably from 
Magas and Bouchardia. In the last-named genus the foramen 
is completely surrounded by the substance of the shell and 
separated from the umbo of the ventral valve, without deltidium, 
while in Waltonia the position of the foramen, deltidium and 
umbo are exactly similar to that of the genus Terebratulina, 
D’Orb. : it approaches also more to Magas by the simplicity of 
its hinge. Besides these particular family characters we find the 
same calcareous support, and the same central elevated plate, but 
more simple in its details. In Magas, besides the two ribbon- 
shaped lamelle described, we find two upper anchor-shaped 
lamellee situated parallel to the under ones: these are net to be 
seen in Waltonia, which has only one pair; while in Bouchardia 
the under ones are completely wanting, and we find only the 
upper or anchor-shaped pair. Thus Magas would be characterized 
by two pair of lamellee, Waltonia by the lower ones only, and 
Bouchardia by the upper ones. In all three the dental portion 
and foramen vary. ‘The punctuation also is less strong in Wal- 
tonia than in Magas, and more so than in Bouchardia. 
On these important differences I think myself authorized to 
propose for this little shell a distinct generic title, and I take 
much pleasure in dedicating it to my old friend William Walton, 
Esq. of Bath. 
Waltonia Valenciennesit, nob. Pl. XV. fig. 1: 
Shell small, of a red colour, ornamented by irregular costz or 
undulations disposed as in Ter. fimbria, the central coste being 
directed towards the umbo, but extending only from the mar- 
gin to about half the length of the valve. The lateral coste, 
instead of being directed towards the umbo as im all plicated 
Terebratule, diverge in a sloping manner towards the middle of 
the shell, and consequently could never reach the umbo (see 
figures). The dorsal valve is more convex than the ventral one, 
which is almost flat, with two ears similar to those visible in Te- 
rebratula Caput serpentis, &e.; foramen large. Length 2} lines, 
breadth 2 lines, depth 1 line; from the seas of New Zealand, 
where Quoy and Gaimard discovered it. 
