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 diiFers 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 Terehratulina, 

 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 lamellae described, we find two upper anchor-shaped 

 lamellae situated parallel to the under ones : these are not 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 lamellae, 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 Valenciennesii, nob. PI. XV. fig. 1. 



Shell small, of a red colour, ornamented by irregular costse or 

 undulations disposed as in Ter. fimbria, the central costse being 

 directed towards the umbo, but extending only from the mar- 

 gin to about half the length of the valve. The lateral costae, 

 instead of being directed towards the umbo as in all plicated 

 Terebratulce, 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- 

 rehratula Caput sej'pcntis, &c. ; foramen large. Length 2| lines, 

 breadth 2 lines, depth 1 line ; from the seas of New Zealand, 

 wliere Quoy and Gaimard discovered it. 



