BY E. M. JOHNSTON, F.L.S. 



115 



dotted ; hinge-line straight, elongated ; umbones 

 anterior, eared, the posterior ear wing-like ; cartilage 

 contained in one or several grooves ; hinge edentulous 

 cr obscurely toothed. 



Genus Avicula. (696-697.) 

 Shell obliquely oval, often thin diaphanous, very inequivalve, 

 eared, the posterior ear produced wing-like ; right valve 

 with a byssal sinus beneath the anterior ear ; cartilage 

 pit single, oblique ; hinge with one or two small 

 cardinal teeth, and an elongated posterior tooth, often 

 obsolete ; posterior muscular impressions (adductor 

 and pedal) large, sub-central ; anterior (pedal scar) 

 small, umbonal. Dist. — -Mexico, South Britain, 

 Mediterranean, India, Pacific, Australasia; 20 fathoms. 



Genus Cbbnatttla. (698.) 

 Shell thin, oblong compressed, byssal sinus obsolete ; cartilage 

 pit shallow, crescent-shaped. Dist. — N. Africa, Bed 

 Sea, China, in sponges. 



Genus Vulsella. (699.) 

 Shell oblong, striated, sub-equivalve, with an inner pearly and 

 outer fibrous layer ; umbones straight, earless. Often 

 found imbedded in living sponges. Dist. — Red Sea, 

 India, Australia, Tasmania. 



(xcvi.) Family Pinnim:. 

 Genus Pinna. (700.) 

 Shell equivalve, wedge-shaped ; umbones quite anterior ; 

 posterior side truncated and gaping ; ligamental groove 

 linear, elongated; hinge edentulous ; anterior adductor 

 scar a.pical, posterior sub-central, large, ill-defined 

 pedal scar in front of posterior adductor. Dist. — 

 TJ. S., Britain, Mediterranean, New Zealand, Tasmania, 

 Australia, Pacific, Panama. 



(xcvii.) Family Spondylid^;. 

 Genus Spondylus. (701.) 

 Shell irregular, attached by the right valve, radiately ribbed, 

 spiny or foliaceous ; umbones remote, eared ; ower 

 valve with a triangular hinge-area, cartilage lin a 

 central groove, nearly or quite covered ; hinge of two 

 curved interlocking teeth in each valve ; adductor 

 impression, double. Dist. — West Indies, Canaries, 

 Mediterranean, India, Australasia, Torres Straits, 

 Pacific, W. America, 105 fathoms. 



