289 AVICULIDA. 
a depression in the other valve; lunular area long, slightly 
gaping, with simple thickened margins, posterior side shorter, 
evenly rounded; muscular scar small, subcentral, semilunar, 
deeply impressed ; surface of shell concentrically lamellar. 
CuarMasiA, Stoliczka, 1870. 
Distr.—Several sp. Cretaceous; Europe. C. Turonensis, Duj. 
Irregularly oblong, longer than high, with prominent obtuse 
beaks ssubequivalve, ‘the valves being slightly convex, ligamental 
groove large, moderately excavated, margin in front of the beaks 
with several irregular incisions, or internal grooves, similar to 
those of Eligmus , muscular scar subcentral, elongated, and 
strongly thickened. 
Munier-Chalmas refers the type species to Vulsella, but in no 
recent or tertiary species of that genus do any incisions or pli- 
cations occur in front of the beaks, nor is the muscular scar 
equally strong in any of them. The shell differs from Eligmus, 
merely by its more compressed form and more centrally placed 
muscular scar and by its thicker shell; it shows greater aflinity 
to Pedum, which has, however, only one incision before the beak, 
and the ligamental pit strongly produced internally. 
Exiagmus, E. Deslongchamps, 1856. 
Etym.—dyp's, a Sinuosity,in allusion to the sinuosities of the 
borders of the post-apical opening. 
Distr.—3 sp. Inferior Oolite, and Great Oolite; Maine-et- 
Loire, Calvados, Galicia. £. polytypus, Desl. (cxxxii, 85-87). 
Shell free, or perhaps attached by a byssus, nearly equivalve, 
inequilateral; ovate or cylindrical, more or less compressed ; 
anterior extremity inflated, and shorter than the attenuated pos- 
terior one. Test rather thick, foliaceous. Umbones inflated, 
slightly depressed or flattened, diverging and directed backwards. 
Valves closed at both extremities, with an unsymmetrical 
(byssal?) sinus behind the umbones; ornamented by oblique, 
radiating carinated ribs; hinge short, straight, edentulous ; 
ligamental area triangular, with a superficial pit; muscular scar 
single, situated on the free end of a spoon-shaped process, 
which originates from beneath the umbonal cavity ; pallial line 
wanting. 
The internal process of Eligmus has no analogy with that of 
the Myze and Anatine, which in them supports the cartilage, and 
is an internal prolongation of the hinge; whilst that of Eligmus 
gives attachment to the adductor muscle, and arises from beneath 
the hinge. Eligmus is related through Chalmasia Turonensis, 
Dujardin, to Vulsella; the test, however, is not fibrous, and M. 
Munier supposes that the internal nacreous layer has been 
destroyed by fossilization. 
