166 PERMIAN FOSSILS. 
This pretty species, which is dedicated to the accomplished founder of the “ Permian 
System,” has some resemblance to the so-called Sanguinolaria truncata, Goldfuss, which 
differs, however, in having a subarcuated hinge-line. It also resembles young specimens 
of Ldmondia unioniformis, Phillips, except that the latter is grooved, and not striated. 
The dorsal and ventral margins of Ldmondia Murchisoniana are nearly parallel to 
each other. The valves are evenly convex, owing to which character the umbones are 
only slightly prominent. A rather long, slightly-developed, curving ridge posteriorly 
bounds the anterior muscular impressions. The cartilage-fulcra (vide Pl. XIV, fig. 17 a), 
when the valves are closed, have a striking resemblance to a Gastrochena,—the 
arcuation of their anterior margin producing a gape resembling that of the latter 
shell. My largest specimen measures an inch in width. 
Edmondia Murchisoniana is a rare species, having only been found in the Shell- 
limestone of Humbleton Quarry and Tunstall Hill. 
Family BAKEVELLIIDS, King. 
The present group appears to be related to Mytilide and Arcide. 
Genus Bakevellia,’ King, 1848. 
Diagnosis.—Aviculoid: biareagerous: inequivalved, the right valve being the 
smallest. Teeth linear; situated at the terminations of the hinge. Cartilage divided ; 
fitting into pits excavated in the hinge-areas. Valves sinuated in the anterio-ventral 
margin for the passage of the foot or byssus. 
Type Avicula antiqua, Minster. 
“This genus is proposed for some inequivalve shells hitherto placed in Avicula. 
It possessed two adductor muscles,” and therefore has no relation to Avicula, which is 
a true Monomyarian :* further, it is furnished with a plurality of cartilage-pits (from 
1 Named after the late Mr. Bakewell; as his instructive ‘Introduction to Geology’ was the first work on 
the subject I read. 
2 Vide Plate XIV, fig. 33a, 6. 
3 Contradictory views are held regarding the number of adductor muscles of Avicula. Deshayes, in the 
last edition of Lamarck (vol. vii, p. 95), states that there is only one ; while Mr. Gray asserts there are two 
(vide Synopsis of the British Museum, p. 118, June 17, 1841): Forbes and Hanley, speaking of the family 
Aviculide, state, that im it “we have a passage from the dimyarian to the monomyarian Lamellibranchiate 
bivalves, great groups, which, though convenient sections, can scarcely be regarded as of ordinal value.” 
(Vide Brit. Moll., vol. ii, p- 250.) The question involved in this passage is of the utmost importance in a 
classification of the Lamellibranchiata ; it is therefore to be regretted that the authors of the ‘ British Mol- 
lusca’ have thus summarily disposed of it. My own examination of a Mediterranean specimen of Avicula 
Tarentina is confirmatory of M. Deshayes’ statement; imasmuch as I have been unable to discover an 
anterior adductor muscle in this shell: those occupying its place are the anterior visceral or pedal muscles : 
the posterior pedal muscles are unusually large, and attached close to, and in front of, the subcentrically 
situated adductor muscle: perhaps the former have been taken for the anterior or extra adductor ? 
