PINNID^. 283 



Family PINNID^. 



Pinna, Linn, 1758. 



Etym. — Pinna, a fm or wing. 



Didr. — 30 sp. U. S., Britain, Mediterranean, Australia, 

 Pacific, Panama. Fossil, 60 sp. Devonian — . Increasing to 

 the present time. II. S., Europe, South India. P. rudis, Linn, 

 (cxxxi, 67). 



Shell equivalve, wedge-shaped ; umbones quite anterior ; pos- 

 terior side truncated and gaping ; ligamental groove linear, 

 elongated ; hinge edentulous ; anterior adductor scar apical, 

 posterior subcentral, 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. 



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

 3^oung it is thin, brittle, and translucent, consisting almost 

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

 and extends less than half-wa}' from the beak. Some fossil Pinnas 

 crumble under the touch into their component fibres. The living 

 species range from extreme low-water to sixty 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, etc. 



A little crab which nestles in the mantle and gills of the Pinna 

 was anciently believed to have formed an alliance with the blind 

 shell-fish, and received the name of Pinna-guardian iPinnoteres) 

 from Aristotle ; similar species infest the Mussels and Anomise 

 of the British coast. 



ATRiNA, Grray, 1840. Shell irregular, valves connate, as though 

 soldered together on the dorsal margin. P. saccata, Linn, 

 (cxxxi, 68). 



PAL^opiNNA, Hall, 1883. Shell gaping in front ; surface marked 

 by fine radiating lines. More convex and with finer rays than 

 in Pinna. 2 sp. Palaeozoic ; N. Y. P. reciiroa, Hall. 



TRiCHiTES, Defrance, 1828. (Pinnigena, Agassiz, 1847) Shell 

 thick, inequi valve, somewhat irregular, margins undulated. 

 Fossil, 5 sp. Oolitic strata of England and France. P. andatus, 

 Lycett (cxxxii, 88 \ Fragments an inch or more in thickness 

 are common in the Cotteswold-hills ; full-grown individuals are 

 supposed to have measured a yard across. 



AVicuLOPiNNA, Meek, 1864. Very elongately subtrigonal, 

 equivalve, with slightly indicated subterminal beaks, the shell 

 being somewhat produced in front of them, posteriorly gaping; 



