COHCaiFEBA. 419 



Inoceramtjs, Sowerby (1814). 



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



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



Synonym, Catillus, Brongn. 



Shell inequivalye, ventricose, radiately or concentrically 

 furrowed, nmbones prominent ; binge-line straight, elongated ; 

 cartilage pits transverse, numerous, close-set. 



This genus difiPers from Perna cbiefiy in form. /. involutus 

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

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

 in the chalk and flints, and are often perforated by the Gliona. 

 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, 1o species. ? Silurian — Chalk. South America, 

 United States, Europe, Algeria, Thibet. 



Pinna, L. 



Etymology, pinna, a fin or wing. 



Tijpe, P. squamosa, PL 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-way from 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. 



