154 PERMIAN FOSSILS. 



Genus Lima, Bruguiere. 



Diagnosis. — " Shell longitudinally oblong, with ears ; beak remote ; Hgament 

 external." (Fleming.)^ 



This genus is not known to have existed previously to the permian period ; but 

 since then it has ever continued to be an inhabitant of our globe. 



Lima Permiana, Kin(/. Plate XIII, fig. 4. 



Diagnosis. — Half an inch in diameter : smooth : oblique towards the posterior 

 direction : somewhat circular : slightly tumid. Hinge-line short. TJmhone small. 



The above diagnosis is taken from a specimen of the left valve, the only one that 

 has occurred to me. At first I took it for a valve of Pecten pusillus, to which it has a 

 close resemblance ; but its obliquity, and the regular sloping sides of its umbone, prove 

 it to be a totally different shell. I have little doubt of its being a species of Lima. 



Humbleton Quarry, in the Shell-limestone, is the only locality that has yielded 

 me this species. 



Family Aviculid^ {Les Arojides), Cuvier, 1800. 



Diagnosis. — "Shell often foliated, generally rather thin, nacreous, subsequivalve ; 

 hinge without teeth, or furnished with some in a rudimentary state ; with an anterior 

 notch for the passage of the byssus." (Sander Rang.)^ 



Genus Monotis, Bronn. 

 AvicuLA, Auct. 



Diagnosis. — " Shell subequivalve, unequilateral, subauriculate, depressed, closed, 

 auricuLited behind, subrotund before. Ear continuous. Umbones depressed sub- 

 mediate. Margin of the hinge linear, callous, without teeth. Canal bending down- 

 ward in an outward direction beneath the umbones, closed on the right valve with an 

 entering fold."^ 



The typical genus of Aviculida has two subcentral muscular impressions in each 

 valve (the posterior or largest belongs to the adductor muscles, and the anterior to 

 one of the posterior divisions of the pedal muscles), a trapezoidal cartilage pit, and a 

 sinus-like byssal opening in the inferior valve. None of the homologous structures are 



^ British Animals, p. 388. 



2 Manuel de I'Histoire, Naturelle des Mollusques, p. 285. 



3 " Testa subsequivalvis, inequilatera, subauricularis, depressa, clausa ; postice auriculata antice rotun- 

 data. Auricula continua. Umbones depressi-submedii. Margo cardinalis linearis, callosus, edentulus, 

 canali sub-umbone antrorsum vergente, in valva dextra a plica intrante obturate. " (Goldfuss, Petrefacta, 

 p. 137.) 



