ACEPHALA TESTACEA. 421 



Panopea, Mesnard, Lagr. 



* A stout tooth, anterior to the callous enlargement of the preced- 

 ing subgenus, and immediately under the summit, which decussates 

 a similar one on the opposite valve, a character which approximates 

 the Panopex to the Solens. A large species is found in the hills 

 at the foot of the Appenines in so high a state of preservation, that 

 it has been mistaken for a recent sea-shel!(l). 



There is another fossil species, which may perhaps be separated 

 from it, that is completely closed at its anterior extremity(2). 



After these various modifications of the Myae, we may place the 



Pandora, Brug. 



In which one valve is much flatter than the other; the internal 

 ligament is placed transversely, accompanied in front by a project- 

 ing tooth of the flattened valve. The posterior side of the shell is 

 elongated. The animal withdraws more completely into its shell 

 than the preceding ones, and its valves shut more closely its habits 

 however are the same. 



But a single species is well known; it inhabits the seas of 

 Europe(3). 



Here also we find a group of some small and singular genera, 

 such as 



Byssomia, Cuv. 



Where the oblong shell, which has no marked tooth, has the opening 

 for the foot at about the middle of its edge and opposite the sum- 

 mits. The Byssomise also penetrate into stone, corals, &c. 



A species which is provided with a byssus, abounds in the 

 Arctic Ocean(4). 



HiATELLA, Daud. 



The shell gaping, to allow the passage of the foot, near the middle 



(1) Mya glycimeris, L., Chemn., VI, iii- A neighbouring, but shorter species 

 inhabits the Mediterranean. Another, fossil species is found near IJourdeaux. 



(2) Panope de Favjas, Mesnard, Lagr., Ann. du Mas., IX, xii. 



Here should be the place of the Saxicata of M. F. de Bellevue, small Testacea 

 which perforate stones. See Roiss., VI, 441. 



(3) Tellina insequivalvis, Chemn., VI, xi, 106, and for the animal, Poli, II, xv, 7. 



(4) 3fyftlus pkoladis, Miill., Zool., Dan., Ixxxvii, 1, 2, 3, or Mya byssifera, 

 Fabr., Groenl. 



