ON IRISH PERMIAN FOSSILS. 
75 
This species has much the aspect of an Avicula, to which many palaeonto¬ 
logists have referred it; specimens, however, have occurred to me completely 
proving it to possess characters diagnostic of a new genus, having some rela¬ 
tion to Modiola, and merely a similitude to Avicula. Thus Avicula possesses 
only one adductor muscle, whereas Bakevellia has been furnished with two, 
the impressions of which are displayed on the specimen (cast) represented, 
twice the natural size, under figure 4 c: they are also visible, but not so 
clearly, in the specimen figured at 4 b. The two muscular impressions are 
connected by a simple pallial scar, exhibited in figure 4 c. The dental cha¬ 
racters, which consist of two elongated teeth—one on each side of the^umbone 
—are well displayed in the cast represented under fig. 4 b. The genus pos¬ 
sesses a cardinal area, with three or more cartilage pits (as in Gervillia, 
Catillus, &c.), which are exhibited in the specimen last referred to. 
Bakevellia antiqua is rather tumid, inequivalve; seldom having its hinge line 
exceeding three-quarters of an inch in length : the surface of the valves, as 
shown by their impressions, is marked with rather prominent lines of growth, 
or striae, parallel to the margin. 
This species is rather common at Tullyconnel and Cultra. It also occurs 
in the Permians of Durham, and the neighbourhood of Manchester. Mr. 
Binney found “ casts of Bakevellia”—probably the same species—along with 
“ Schizodus, and other shells,” in the magnesian limestone at Barrow Mouth, 
between St. Bees’ Head and Whitehaven in Cumberland.* It is a character¬ 
istic fossil in Germany and Russia. Other four species are known to occur in 
the Permian system. The genus is also represented in the carboniferous and 
saliferous rocks; the so-called Avicula socialis, common in the Muschelkalk, 
is a Bakevellia. 
6. Pleukophorus costatus = Area costata , Brown. —PI. i., figs. 5 a, b; Mono¬ 
graph, pi. xv., figs. 18, 20. 
This shell is the type of an equivalved genus, first proposed in my Mono¬ 
graph, having some relation to Cardita. It is furnished with two diverging 
cardinal teeth in both valves, and one elongated posterior tooth in the right 
valve. The specimen represented under figure 5 a, is a cast of the right valve 
exhibiting the groove (a ridge in the cast) into which the posterior tooth of the 
right valve fitted; but it does not display so clearly the impressions of the car¬ 
dinal teeth, which, however, are distinctly seen in one or two specimens before 
me. The anterior adductor muscular scar (in the present species deeply ex¬ 
cavated) is bounded posteriorly by a ridge, the impression of which, as well 
as that of the muscular scar, are seen at * in the same figure. 
Pleurophorus costatus is oval, and veiy inequilateral: it is generally orna¬ 
mented with three or more ribs, running from the umbone to the posterio-ven- 
tral margins, and with a number of raised lines, running parallel with the free 
* “ On the Permian Beds of the North-west of England,” vol. xii., Memoirs of 
the Literary and Philosophical Society of Manchester. 
