WILSONIA. 135 
Sowerby, in the ‘Geol. Trans.,’ are nothing more than shapes of Rh. cuboides. 
The species seems sufficiently distinct, and, while varying in width and in the 
number of its ribs, is marked by its low and small beak, its shallow ventral valve 
with high reflexed shoulders, its dorsal contour, which is slightly convex above 
and rather rounded below, and by the depression of its lower margins and the 
median lineations on the ribs in that part. 
Eh. pugnoides, Schnur, seems to agree with this form rather than with 
Rh. pugnus. 
There is very little difference from it in Rh. procuboides, Kayser,’ as shown by 
the fact that that learned author, while referring Davidson’s figure of the 
Lummaton shell to Rh. cuboides,? quotes the shell as found by himself at 
Lummaton as Rh. procuboides.2 I am not, however, prepared to question his 
differentiation of the Eifel shell, but only to maintain that the Lummaton shell is 
the true Ih. cuboides. 
Whiteaves (loc. cit.) has some interesting remarks on the synonymy, in which 
he includes Rh. intermedia, Barrois, Rh. Hmmonsi, Hall and Whitfield, and 
Rh. venustula, Hall. 
2. WILSONIA OMEGA, n. sp. Pl. XV, figs. 5, 5a, 55. 
Cf. 1867. RuyNcHONELLA veNustTULA, Hall. Pal. N. Y., vol. iv, p. 346, pl. liv a, 
figs. 24—43. 
Description.—Shell spheroidal. Beak rather large, narrow, and recurved. 
Dorsal evenly convex, with a low narrow fold. Ventral valve rather deep, with 
oblique sides. Lateral margins straight. Front margin very much elevated, 
forming a high rectangular sinus. Ribs short and widely grooved near the 
margins. 
Size.—Height, 17 mm.; width, 18 mm.; depth, 16 mm. 
Remarks.—Sowerby, in the ‘ Geol. Trans.,’ figures a shell of Mr. Hennah’s, 
now in the Collection of the Geological Society, under the name of A. spherica. 
This specimen Davidson regards as a Silurian fossil accidentally mixed with 
Mr. Hennah’s specimens, and therefore excludes it from the Devonshire lists. In 
the Wenlock Limestone are found specimens which he considers identical, and 
refers to as th. Wilsoni, var. Davidsoni, M‘Coy, as Sowerby had himself described 
' 1871, Kayser, ‘ Zeitsch. Deutsch. Geol. Gesell.,’ vol. xxiii, p. 513, pl. ix, figs. 3a, 6; and 1883, 
Kayser in Richtofen’s ‘ China,’ vol. iv, p. 78, pl. ix, fig. 2 = Rh. cuwboides in 1854, Schnur, ‘ Paleonto- 
graphica,’ vol. il, pl. xlv, fig. 4 (only). 
2 1871, Kayser, Zeitsch. Deutsch. Geol. Gesell., vol. xxiii, p. 514. 
3 1889, Kayser, ‘ Neues Jahrb. f. Min.,’ Band i, p. 186. 
