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( io ) 



DIVISION XIV. MYTlLACEvE. 



GENERA. (1) 



d. Modiola. Lam. M. 



Shell sub -transverse, No teeth ; hinge late- Ligament almost in- 



equivalved, regular, pos- ral and linear. terior, received in a 



terior side very short : marginal furrow : mus- 



beaks almost lateral, in- cu!ar impression sub- 



clined on the short side. lateral, elongated. (2) 

 Fig. 64. 



2. LlTHODOMUS. Cll\>. M. 



Almost equally rounded 

 at both ends : beaks near the 

 posterior end. (3) Fig. 65. 



3 . Myt ilus. (4) L in . M . F . 



Equivalved, regular, 

 pointed at the base ; fixed 

 by a byssus ; beaks al- 

 most straight, terminal, 

 pointed. Fig. 66. 



a . Shell furrowed longitudinally, 

 j?. No longitudinal furrows. 



4. Pinna. Lin, M. 



Longitudinal, wedge- 

 shaped, equivalved, ga- 

 ping at the summit, point- 

 ed at the base; beaks 

 straight : byssus extreme- 

 ly fine and silky. Fig. 67. 



Ligament marginal, 

 linear, very long, almost 

 interior. (5) 



(i) The greater number of Mytilacece attach themselves to marine bodies, by a byssus. 

 ('2) These do not attach themselves by a byssus. Foss. in the London Clay, 

 Green Sand, Upper Oolite, C lunch Clay, Alum Shale, Blue Lias, at Grignon, 

 Plaisance, Vaches-Noircs, St. Jean d'Asse, Chauffour, Dom front, Tanrie. 



(3) Lamarck does not admit this as a distinct genus. They have a byssus, 

 which does not grow after they have lodged themselves in stone. Ihe manner in 

 which the Litlwdomi, Pholades, and some others, hollow out the stones which 

 they inhabit, has given place to much discussion: some believe it to be effected by 

 the mechanical action of the valves; others by dissolution. One of the Litlwdomi 

 is very common in the Mediterranean, where it is esteemed from its agreeably 

 pungent taste. 



(4) Towards the end of autumn, we frequently find small crabs, who take 

 shelter in the shells of the Mytili, without injuring the animal. M. de Ferussac 

 has shewn me what is supposed to be a fresh-water Mytilus. They are frequently 

 eaten, but are dangerous in any quantity. Besides the cardinal, they have a 

 thinner ligament, fixed within, towards their superior extremity. Dr. Leach 

 first determined its use to be that of moderating the effects of the elasticity of the 

 cardinal ligament, without obliging the muscle of attachment to contract itself: 

 there is another at the base of the shell, which probably strengthens the cardinal 

 attachment. The Mytiloides found in while chalk and chalktufau, is so thin and fragile, 

 and adheres so closely to the rock in which it is found, that the hinge is unknown, 

 and it is merely placed temporarily with the Mytili^ from its apparent resemblance. 

 It varies considerably in form and size, and the folds are sometimes very delicate. 

 Vide fig. 68. 



(5) The byssus of the Pinna is lonp, fine, lustrous, silky, and full ; it takes 



