FAMILY 4. PECTINACEA. 155 



planiuscula, lateribus simplicibus, subincrassatis. Cardo edentulus, 

 ligamento interno, in fossula trigona, centrali, inserto. 



The Pedum was arranged by Linnaeus in his genus Ostrea ; but, from 

 the remarkable and peculiar construction of the shell, Bruguiere was 

 induced to distinguish it in the ' Encyclopedic Methodique ' by the above 

 new generic title. In this he was quickly followed by Lamarck ; and 

 although the animal was still unknown, its shell presented so distinct an 

 assemblage of characters, that no one could fail to appreciate the genus 

 that was now fairly established. Since then the anatomy of the Pedum 

 has been fully described by MM. Quoy and Gaimard in the ' Voyage de 

 l'Astrolabe,' and it singularly accords with what Lamarck had anticipated 

 while placing it at the commencement of the family. The organization 

 of this animal appears to be exactly intermediate between that of Avicula 

 and Spondylus : like the former, it is provided with a strong tendinous 

 byssus exserted in the same direction ; and the shell, like that of the 

 latter, no longer exhibiting that particular fibro-laminar structure, forms 

 a solid umbonal area. Its habits, however, appear to differ considerably 

 from both, as many of them were found by this indefatigable naturalist 

 partially buried in Madrepores, in crevices of their own boring. 



The shell of Pedum may be described as being longitudinal or elon- 

 gately hatchet-shaped, inequivalve, and slightly auriculated ; the valves 

 are both produced at the base into a triangular disc, increasing with age, 

 in the centre of which is a groove or pit, projecting inwardly for the 

 reception of the ligament ; the lower valve is rather convex, with the 

 sides reflected over ; but the upper valve is flatfish, and simple or some- 

 what thickened at the sides. 



Example. 



PL CXI. Fig. 1 to 5. 



Pedum Spondyloideum, Lamarck, Anim. sans vert., new edit., vol. vii. 



p. 112. Enc. Me'th., pi. 178. f. 1. De Blainville, Manuel de Mala- 



cologie, pi. 62. f. 6. Quoy, Voyage de l'Astrolabe, Mollusques, pi. 76. 



f. 15 to 21. 



Ostrea Spondyloidea, Gmelin. 



x2 



