CONCniFEBA. 419 



Inoceramits, Sowerby (1814). 



Etymology, is (inos), fibre, heramos, shell. 



Example, I. sulcatus, PL XYII., Fig. 3. 



Synonym, Catillus, Brongn. 



Shell inequivalve, yentricose, radiately or concentrically 

 furrowed, umbones prominent ; hinge-line straight, elongated ; 

 cartilage pits transverse, numerous, close-set. 



This genus differs from Perna chiefly in form. /. involutus 

 has the left valve spiral, the right opercular. /. Cuvieri attains 

 the length of a yard. Large flat fragments are common both 

 in the chalk and iGlints, and are often perforated by the Cliona. 

 Hemispherical pearls have been found developed from their 

 inner surface, and spherical pearls of the same prismatic- cellular 

 structure occur detached, in the chalk. (Wetherell.) The Ino- 

 cerami of the gault are nacreous. 



Fossil, 15 species. ? Silurian — Chalk. South America, 

 United States, Europe, Algeria, Thibet. 



Plnna, L. 



Etymology, pinna, a fin or ■wing. 



Type, P. squamosa, PI. XYL, Fig. 23. 



Shell equivalve, wedge-shaped ; umbones quite anterior ; 

 posterior side truncated and gaping ; ligamental groove linear, 

 elongated ; hinge edentulous ; anterior adductor scar apical, 

 posterior sub-central, large, ill-defined ; pedal scar in front of 

 posterior adductor. 



Animal with the mantle doubly fringed ; foot elongated, 

 grooved, spinning a powerful byssus, attached by large triple 

 muscles to the centre of each valve ; adductors both large ; palpi 

 elongated ; gills long. 



Distribution, 30 species. United States, Britain, Mediter- 

 ranean, Australia, Pacific, Panama. 



Fossil, 60 species. Devonian — . United States, Europe, 

 South India. 



The shell of the Pinna attains a length of two feet ; when 

 young it is thin, brittle, and translucent, consisting almost 

 entirely of prismatic cell-layers ; the pearly lining is thin, 

 divided, and extends less than half-waj'- fi-om the beak. Some 

 fossil Pinnas crumble under the touch into their component 

 fibres. The living species range from extreme low water to 

 60 fathoms ; they are moored vertically, and often nearly buried 

 in sand, with knife-like edges erect. The byssus has sometimes 

 been mixed with silk, spun, and knitted into gloves, &c. (Brit. 



