ANIMALS. 169 
Diagnosis.—“ Shell subrhomboidal, arched, smooth ; front wing acute, hinder one 
obtuse angulate.”’ (Miinster.) 
Probably Count Minster drew up the above diagnosis from a smooth variety, or a 
specimen divested of its testaceous covering,—a rather common case ; as this species 
is quite as much striated as the last. 
Dr. Geinitz has merged Bakevellia antiqua into B. ceratophaga ; but there is clearly 
sufficient difference between them to warrant their separation. The present species 
differs from 2. ceratophaga in bemg a more tumid shell; in having the valves thicker, 
the umbones more divaricated, the hinge-areas larger, the sinus in the wing-areas 
much smaller, the wing less produced, the byssal or pedal sinus only slightly marked, 
the incremental striz more regular, and the anterior lobes and wing-areas decidedly 
less obviously separated from the convexity of the valves. It also attains a larger 
size. My largest specimen is an inch and a quarter in width, that is, in the direction 
of the hinge, and seven eighths of an inch in length. 
Owing to the thickness of the valves of Bakevellia antiqua, the muscular impressions 
are so strongly marked, that casts occasionally display them in the most instructive 
manner. ‘The cast represented in Pl. XIV, fig. 33, particularly enabled me to decide 
that the species had no relation to the genus in which it had usually been placed: the 
anterior and posterior adductor muscular impressions (@, 4) and the pallial line (¢) are 
so well marked, that there can be no doubt of its being a true Dimyarian. 
Notwithstanding the thickness of the valves, both are strengthened internally on 
the anterior side of the umbonal cavity with a slight ridge, which posteriorly bounds 
the anterior adductor muscular impression. 
Bakevellia antiqua has some resemblance to young specimens of the Carboniferous 
Gervillia lunulata, Phillips. It is in some localities a rather variable species, particu- 
larly in the neighbourhood of Manchester, where specimens occur varying much in the 
divarication of the umbones. Captain Brown has been led to regard these varieties, 
from an examination of some imperfect and in many cases distorted casts, as different 
species; but I feel persuaded, after carefully examining the original specimens, 
including others contained in various collections, that they are all referable to the 
present species. 
Bakevellia antigua is a widely distributed species, and appears to be characteristic 
of every member of the Permian system. It occurs in the Shell-limestone of 
Humbleton Quarry, Hylton North-Farm, Southwick-lane House, Dalton-le-Dale, 
Ryhope Field-House Farm, Tunstall Hill, Silksworth, and Castle Eden-Dene; in the 
probably contemporaneous Breccia at the north end of Black Hall Rocks; and in 
the lowest beds of Whitley Quarry. It is found in the Permian Marls at Bedford, 
Collyhurst, and Newtown near Manchester (Binney) ; also at Woodhall, Stubbs Hill, 
. 1 “Avicula testa subrhomboidali fornicata leevi, ala antica acuta postica obtusangula.” (Goldfuss, 
Petrefacta, 2d part, p. 126.) 
W 
