FAMILY 3. AVICULACEA. 149 



superne depressum, cum fovea conica, oblique arcuata, desuper im- 

 pressum, iigamento inserto. Impressio muscularis subcentralis, 

 propius ad basem distincte imbuta. 



We are certainly at a loss to determine why the great author of the 

 1 Systema Naturae' included the Vulsella? in his genus Mya, unless he sup- 

 posed that some analogy existed between the prominent ligamentiferous 

 process of the former, and the spoon-shaped tooth of the latter. They 

 were placed by Bruguiere, his immediate successor, in the genus Ostrea; 

 and even Lamarck retained them in his family of ' Les Ostracees,' though 

 separated from the Ostrea under a new generic title. Cuvier was the 

 first to note the affinity that exists between the shell of the Vulsella? and 

 that of the Mallei, he therefore removed them to their immediate vicinity ; 

 an improvement in the classification which subsequent authors have not 

 failed to appreciate. Their shell is of the same thin fibro-laminal com- 

 position as that of the rest of the family, and the hinge is certainly a 

 modification of that of Malleus. The Vulsella? are generally found in 

 sponges ; the animal is still unknown, nor has it been yet ascertained 

 whether it is provided with a byssus. From its peculiar mode of habita- 

 tion, we can hardly be inclined to suppose that one is required. 



The shell of Vulsella is described as being longitudinal or lingulate, 

 equivalve and rather irregular, with the umbones equal. The ligament 

 forming the hinge is partly external, attached to a groove, which crosses 

 a somewhat depressed triangular disc ; and partly internal, inserted in a 

 conical obliquely-curved process or pit projecting within the valves ; the 

 muscular impression is oblong and subcentral, inclining towards the base 

 of the shell. 



This triangular disc or area is the commencement of a new character, 

 arising from the manner in which the hollow of the valves advance, as it 

 were, with the increase of the shell, carrying the ligamentiferous process 

 forward. The early growth then forms a kind of solid disc, showing the 

 decayed remains of the original ligament in the groove which is left by 

 the advance of the ligamentiferous process. This peculiarity of growth, 

 however, is much more fully developed in the shells of the Pectinacea, in 



