278 AVICULID. 
CrenaTuLa, Lamarck, 1802. 
Syn.—Dalacia, Gray, 1848. 
Distr.—8 sp. N. Africa, Red Sea, China—in sponges. Fossil, 
4sp. Jurassic. C. viridis, Lam. (cxxxi, 65). 
Shell thin, oblong, compressed, byssal sinus obsolete; cartilage- 
pits shallow, crescent-shaped. 
? Leproconcna, Giebel, 1856. 
A small, roundish shell, with the lamellar structure of an 
Ostrea, umbones nearly central, as in Brachiopoda, outer 
surface tubercular, hinge-area with three to four ligamental (?) 
grooves 
The above name has been proposed for a small Triassic shell 
which Giebel says comes near to Plicatulaor Pulvinites. If the 
hinge-grooves are ligamental, as they are supposed to be, the 
classification of this genus would be near Pulvinites; but better 
material must be examined, in order to define the characters of 
both these problematic genera. 
PrrnostrEA, Munier-Chalmas, 1864. 
Distr.—6 sp. Jurassic; Europe. P. Bachelieri, M.-C. (cxxx,54). 
Shell rounded or oval, solid, more or less tumid, inequivalve, 
the left valve being in adult specimens attached ; str ucture lamellar, 
resembling that ‘of Perna; beaks usually indistinct, hinge-area 
broad, or with age becomes more or less reduced in extent, with 
numerous (4-8) transverse ligamental grooves or pits, as in 
Perna; muscular impression rather small, subcentral, ovately 
rounded, in the right valve. This genus forms a , connecting link 
between Perna and Ostrea, ditlering from the former especially 
by its sessile habitat, absence of a byssal sinus and strongly exea- 
vated muscular sear, from the latter by the presence e of separate 
ligamental grooves. Externally Pernostrea is barely distinguish- 
able from Ostrea. 
INocERAMUS, Sowerby, 1814. 
Etym.—Is (inos), fibre; keramos, shell. 
Syn.—Mytiloides, Brongt. 
Distr.—Fossil, 75 sp. ?Silurian, Trias—Cretaceous; South 
America, United States, Europe, Algeria, Thibet. J. concentricus, 
Sowb. (cxxx, 55). 
Shell inequivalve, ventricose, radiately or concentrically fur- 
rowed, umbones prominent; hinge-line straight, elongated ; car- 
tilage-pits transverse, numerous, close-set. 
This genus differs from Perna chiefly in form. J. involutus 
has the left valve spiral, the right opercular. J. Cuvieri attains 
the length of a yard. Large “flat fragments are common both 
in the chalk and flints, and are often perforated by Cliona. 
