168 SUPPLEMENT. 



casionally moors itself by a byssus. The colour of the soft 

 parts is not less variable than that of the shell. When it is 

 at rest, the mantle forms a thick semicircular cushion, striped 

 across with yellow, brown, red, pink, and every intermediate 

 hue. Cornwall (Hockin). F. Monte Mario (Rigacci). E. 

 Mediterranean electric-telegraph cable, at a depth of over 

 1000 f. (Milne-Edwards). 



P. 69. — P. steiatus. Plymouth (Jordan) ! F. Scandinavia 

 and Italv ! E. Med. and Adr. ! 



P. 71. — P. similis. Shetland, 95 f. E. N.W. Germany 

 and Italy. E. LofFoden I., 300 f. (Sars) ; Arcachon (Lafont) ! ; 

 Jamaica (Barrett) ! P. squama, Scacchi, and P. pullus, Can- 

 traine. Not P. Actoni, which is the P. concentricus and P. 

 fenestratus of Forbes, P. Philippii of Acton, and P. incequi- 

 sculptus of Tiberi. 



P. 73. — Add P. vi'tretts*, Chemnitz (Pallium vitreum, 

 Chemn. Conch. Cab. vii. p. 335, t. 67. f. 637, a). 



Shell circular, except at the top, where the outline is 

 square, equilateral, equivalve, rather tumid, extremely thin 

 and fragile, scarcely glossy : sculpture, microscopic and very 

 numerous hair-like striae, which radiate from the beak to the 

 margins, those on the larger ear being horizontal, stronger, 

 and more remote ; there are also much less numerous slight 

 concentric lines, which are closely but irregularly studded with 

 minute vaulted scales ; these scales are not present on every 

 part of the shell, and are sometimes almost wanting ; the an- 

 terior ear of the lower valve is marked with about half a dozen 

 horizontal and crenellated riblets, some being also observable 

 on the anterior or byssal slope in that valve, and the upper 

 margin of the same ear, as well as the edge of the anterior 

 slope, are serrated or toothed : colour white : beaks minute, 

 calyciform : ears, all except that on the anterior side of the 

 lower valve broadly triangular, and not distinctly defined; 

 the anterior ear of the lower valve is of a more irregular 

 shape in consequence of the byssal excavation or notch at the 

 base : bt/ssal notch large : hinge-line straight, -| of the breadth 

 of the shell : cartilage small : hinge-plate broad and smooth : 

 inside nacreous, minutely striated lengthwise in the middle : 

 muscular scars conspicuous. L. 0*4. B. 0*35. 



* Glassy. 



