284 SPONDYLID^. 



hinge-line very long, edentulous. Avic. prisca, Mtinst. (cxxxii, 

 89), from permian rocks. 



Bryophila, Carpenter, 1864. 



Distr. — B. setosa, Carp. On algse, at Cape St. Lucas, L. 

 California. 



Shell like a minute Pinna, with pointed beaks ; upper margin 

 straight, with a strong internal ligament, anteriorly at the byssal 

 sinus somewhat insinuated, ventrally and posteriorly rounded 

 and gaping; posterior muscular scar subcentral, indistinct. 



The animal is stated to be viviparous ; and in form " like a 

 minute Pinna, or a transverse Margaritophora without ears, or 

 a Perna without pits." Its length is only 0"13 inch and the 

 width 0"2 inch, but it is said to be adult. The structure of the 

 shell agrees with that of Pinna, being fibrous externally, nacreous 

 internally. 



Suborder MONOMYARIA. 



Shell with a single subcentral or subposterior muscular 

 impression. 



(Pectinacea. ) , 



Family SPONDYLID^. 



Shell inequivalve, right valve largest, attached at the beak ; 

 cartilage internal, in a median pit ; hinge-teeth two in each valve, 

 sometimes without teeth ; outer surface with radiating ribs, 

 often spiniferous. 



Plicatula, Lamarck, 1801. 



Etym. — Plicatus, plaited. 



Distr. — 9 sp. W. Indies, India, Philippines, Australia, West 

 America. Fossil, 106 sp. Trias—; United States, Europe, 

 Algeria, India. P. Mantelli, hea,, AlsibsiTaa,, has the valves eared. 

 P. ramosa, Linn, (cxxxi, 69}. 



Shell irregular, attached by the umbo of the right valve ; valves 

 smooth or plaited : hinge-area obscure ; cartilage quite internal ; 

 hinge teeth two in each valve ; adductor scar simple. 



Animal resembles Spondylus. 



HARPAX (Parkinson, 1811 ), Deslongchamps, 1858. Hinge of 

 attached valve consisting of a flattened triangular plate, 

 traversed by a central more or less perpendicular ligamental 

 furrow, exterior to which are slightly marked diverging sulci to 

 receive the elevated borders of the ligamental groove in the 

 other valve; the outer borders of the plate form lengthened and 

 elevated dental processes. Hinge-plate of free valve traversed 

 mesially by the ligamental groove, the borders to which are 

 elevated and but slightly diverging ; exterior to these are 



