204 BRITISH SILURIAN BRACHIOPODA. 
Merista ? cYMBULA, sp. nov. Pl. XXII, figs. 28, 29. 
Spec. Char. Shell very small, elongated, oval, or subrhomboidal, greatest breadth a 
little below the middle. Ventral valve evenly convex, forming a nearly regular arch from 
the beak to the frontal margin, slightly subcarinate ; beak small, strongly incurved over the 
umbone of the dorsal valve. Dorsal valve concave, slightly convex at the umbone and 
lateral edges. Surface of both valves smooth. In the interior of the ventral valve a 
triangular arched plate, with a projecting ridge along the middle, commences under 
the extremity of the incurved beak and extends to about half the length of the valve; on 
either side of the beak a strong tooth is supported by a curved dental plate. Interior of 
dorsal valve not known. 
Length 2, width 13, depth 1 line. 
Obs. The genus to which this curious little shell should be referred cannot yet be 
determined, for we know nothing of the internal arrangements of its smaller valve. It 
resembles much, in its external appearance, a shell described and figured by Mr. 
Billings im the ‘Canadian Journal’ for May, 1861, under the designation of Centronella 
glans-fagea, Hall;’ but this last differs from ours by its much larger dimensions and 
more prominent beak. While describing his Rhynch. glans-fagea, Professor Hall remarks 
that it differs so widely from any other species hitherto found in his (American) rocks as 
to be at once recognised merely by its form, and that he has placed it provisionally in 
the genus Rhynchonella; not having had an opportunity of seeing its internal characters. 
In 1859 Mr. Billings mentioned this species as the type of his new genus Centronella, and 
he considered it to be intermediate to Terebratula and Waldheimia on account of its simple 
loop, which extends to about half the length of the valve before being reflected back- 
wards towards the beak. Not knowing what are the characters of the interior of the 
dorsal valve of our shell, I cannot surmise whether or not it possessed a loop; and as 
Mr. Billmgs does not mention the presence of an arch-shaped plate in the ventral valve of 
C. glans-fagea, it is probable that our British shell does not belong to the same genus. 
The arch-shaped plate of J. ? cymbula resembles somewhat that figured by Prof. Hall in 
his Camarium typum or that of some species of Merista. We will, therefore, for the 
present, leave it under the last-named genus. 
Position and Locality. 'This little shell was found in the Caradoc-Bala formation 
at Hendre wen (Cerrig-y-druidion) ; and I believe it occurs also at the Chair of Kildare, in 
Ireland, in the same formation. 
} Rhynchonella ? glans-fagea, Hall. ‘Tenth Annual Report of the Regents of the University of the 
State of New York,’ p. 85, 1857. 
