258 PATELLID^E. 



the upper surface there are three other lead-coloured bands, 

 varying in breadth ; the one immediately above the foot is 

 narrow and faint; the next is the broadest, and takes the 

 shape of the circular muscle, distinctly shadowing out its 

 strong, thick-set, transverse muscular filaments; the upper- 

 most is narrow, and the most intense in colour. The mantle 

 within is white, and between its margin and the body is placed 

 the branchial cordon of 80-100 white subtriangular plates, 

 margined at the outer edges, and so extremely close-set as to 

 present the appearance of mere thread-like filaments without 

 depth ; these line ^-ths of the circumference, passing round the 

 posterior end, where they are largest, diminishing gradually 

 anteally, until they are interrupted by the head. 



I am of opinion with Professor Forbes, that this cordon is 

 only an elongated branchial plume springing from the neck, 

 and ought not to be looked on as a pair of symmetrical sub- 

 semicircular laminae, as in the cyclobrauchiate Chitons. I 

 think this view is confirmed by the animal having the ven- 

 tricle accompanied by only one auricle instead of two, as 

 in Chiton. The heart and aimcle does not span the in- 

 testine, as in nearly all the Bivalves, and in the last section. 

 This is a remarkable departure from the usual structure, 

 and indicates an approach to the more advanced Gastero- 

 poda, and points out that Patella ought to follow Fissurella 

 and Emarginula. The head is a plain subcircular muzzle, 

 under which is the oval, puckered, hollowed-oiTt mouth with 

 a vertical fissure ; and, within, the corneous plates may be 

 seen, supporting the lead-coloured palate, and the very long, 

 narrow, light yellow spinous tongue passing through the 

 oesophagus, that is spirally coiled in the stomach, which 

 pursues its course as an intestine, with many circumvolu- 

 tions entwined with the liver, which in this species is a 

 light green granular mass ; near the posterior end it doubles, 

 and, accompanied by the oviduct, terminates a little to the 

 right of the neck under the teiitaculum, and not, as is more 

 usual, lower in the side of the body, and more posterior; 

 the anal tube and the oviduct march together to the right 

 side, the former being double the size of the latter. The ten- 



