( 4 ) 



# 



DIVISION I. PHOLADAMjE, 

 GENERA. (1) 



4. Pholas. Lin. T. 



Transverse, gaping at A plate from each Ligament exterior, 

 each end ; generally white valve, projecting into with accessory pieces 

 and striated. Fig. 1. the other valve. distinct from the valves. 



(2) 



DIVISION II. L1THOPHAGL 



GENERA. 



4. Gastroch&na, Spen- 

 gler. T. 



Gaping at both ends, 

 but at one much more 

 than the other : very fra- 

 gile. (3) Fig. 2. 



2. Byssomia. Cuv. M. 



Oblong, opening oppo- 

 site'to the beaks. Fig. 43. 



3. Petricola. Lam. M. 



Sublrigonal, inequilate- 

 ral; one end rounded, 

 the other gaping. Fig. 5. 



Hinge linear, mar«- 

 ginal. 



Hinge without teeth. 



Hinge with 2 teeth on 

 one valve, and 1 on the 

 other, or 2 on each. (5) 



Ligament exterior. 



Ligament exterior r 

 with a byssus. (4) 



Ligament exterior. 



(1) Where the habitat is not mentioned, the genus is found in the seas and dif- 

 ferent climates of both hemispheres : T- indicates that it is terrestrial; M. marine; 

 F. f hi viatic. 



(2"! Some of these accessory pieces are attached to the hinge, and cover the liga- 

 ment exteriorly ; others are within, fixed under the beaks. The animals pierce 

 stone or wood, or bury themselves in the sand; they are generally stationary in 

 the holes which they have bored, and the shell is very fragile. They have been 

 much sought for on account of their agreeable flavour ; some species are found on 

 the coa.-.ts of France. Fcss. in Crag Marl, London Clay. 



(3) They pierce and live within madrepores. The animals of this Division 

 bury themselves, with their anterior extremity always near the mouth of the 

 hole which contains them, ready to receive the water. 



(4) One species is very abundant in the Northern Seas, and is provided with a 

 byssus. 



(5) Lamarck formerly divided this genus into Petricola and Rupellaria; but the 

 variations he has subsequently discovered in their hinges, have induced him to 

 reunite them. They inhabit stones, Foss. in Italy, at Pont Levois. 



