RHYNCHONELLID. 173 
author had previously, in the ‘Silurian System,’ applied that name to a slightly varied 
form of Rhynchonella deflewa: it will therefore be better to adopt M‘Coy’s term Davidsoni 
as a varietal designation for the modification of R/. Wilsont under description. — Prof. 
MCoy, in his work on ‘ British Palaeozoic Fossils,’ refers to the figure given by myself in 
the ‘ Bulletin de la Société Géologique de France,’ vol. v, pl. ii, fig. 36, as the type of 
his Hem. Davidsoni. I mention this because in the Woodwardian Museum some very 
uncertain examples had been so named by Prof. M‘Coy. 
The variety Davidsont occurs in the Wenlock Limestone at Dudley, Walsall, me 
Falfield. Prof. M‘Coy states it to be very rare in the Upper Ludlow rock of Burton and 
Brockton, near Wenlock. 
RHYNCHONELLA WILSONI, var. SPH#ROIDALIS, M‘Coy. Pl. XXIII, fig. 10. 
HerMITHYRIS SPH#ROIDALTS, M‘Coy. Annals and Mag. of Nat. Hist., vol. viii, 2nd ser., 
p- 393, 1851; and Brit. Pal. Foss., p. 206, pl. i, 
fig. 4, 1852. 
As already stated, judging from the description and figure published by Prof. 
M‘Coy, Hemithyris spheroidalis can be nothing more than a small variety or young 
form of Rhynchonella Wilsoni. It occurs in the Wenlock Limestone of Dudley, and in 
the Aymestry Limestone of Sedgley and of Botville. 
RuHYNCHONELLA Nasuta, M‘Coy. Pl. XXIII, fig. 19. 
Hemituyris nNasuta, A‘Ooy. Annals and Mag. of Nat. Hist., vol. viii, 2nd ser., 
p. 393, 1851; and British Pal. Foss., p. 203, pl. i 1, ii, 
fig. 5, 1852. 
Spec. Char. Longitudinally oval, either longer than wide or about as wide as long ; 
sides rounded ; the front in old specimens is produced into a flat tongue-shaped lobe. Valves 
almost equally convex, the dorsal one slightly the deepest. In the ventral valve the sinus 
commences close to the extremity of the beak, and gradually widens as it nears the front ; 
beak moderately produced, and so much incurved as to almost touch the umbonal beak of 
the opposite valve. Dorsal valve uniformly convex at the umbone, but gradually a wide 
obtusely rounded mesial fold is produced, so that the valve becomes trilobed anteriorly. 
Surface ornamented with from twenty to twenty-six simple, close, slightly produced, 
rounded, radiating ribs, of which six or seven, rather stronger than the rest, occupy the fold 
and sinus. Interior not known. ‘Two specimens measured— 
Length 14, width 12, depth 8 lines. 
yy!) ERs orgy 1D Limes: 
