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DIVISION XVI. PECTINIDES. 



GENERA. 



1. Pedum. Lam. M. 



Inequivalved, a little 

 auricular, gaping and 

 sloped at its inferior valve : 

 beaks unequal, wide apart. 

 Fig. 78. 



2. Lima. Brug. M. 



Longitudinal, sub-equi- 

 valved, auricular, a little 

 gaping on one side, beaks 

 wide apart. Fig. 79. 



3. Placiostoma. Sower- 



by. Foss. 



Sub - equivalved, sub- 

 auricular ; base, trans- 

 verse, straight ; beaks 

 somewhat distant, their 

 interior sides in transverse 

 furrows flattened exter- 

 nally, one straight, the 

 other inclined obliquely : 

 shell thin. Fig. 82. 



4. Pecten. Lam. M. 



Regular, inequivalved, 

 auricular, lower edge 

 transverse, straight; beaks 

 contiguous. Fig. 80. 



a. Ears equal or almost equal, 



Hinge without teeth. 



Ligament partly exte- 

 rior, inserted in an ob- 

 long channelled hollow, 

 sunk in the interior of 

 the beaks. (1) 



Ligament partly ex- 

 terior, received in a car- 

 dinal hollow* (2) 



Ligament received in 

 a conical cardinal hol- 

 low below the beaks, 

 partly interior, opening 

 without. (3) 



Ligament received in 

 a triangular, interior, 

 cardinal hollow. (4) 



0. 



unequal. 



(1) There is but one species known, which conies from the Isle of France, and 

 the Indian Seas ; it is very rare and precious. 



(2) There is a beautiful species in the Mediterranean, the animal of which is 

 eaten. Foss. in the Under Oolite ; Grignon, Italy, Marl-pits of Touraine. 



(3) These shells are difficult to recognise, from the hard stone which fills 

 them ; they are only known in a fossil state, and are found in the Upper Chalk, 

 Lower Chalk, Blue Lias, White Lias, Portland Rock, Kelloway Stone, Upper Oolite, 

 Fuller' 's-earth Rock, and at Carantan, Manicrt, Chateau dc Loir, Bourdeaux. 



(4) The greater number are ornamented with brilliant and various colors; one 

 species, the Ostrea maxima of Linnaeus, is eaten. Foss. in the Lower Cha'k, 

 Green Sand, Chalk Marl, Kelloway Stone, Bedford Limestone, Upper Oolite, Under 



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