406 CHITONID^. 



coating; whence, probably, the idea of its occasionally 

 sombre hue has arisen, since none of the specimens exa- 

 mined by ourselves could be termed (as the species has 

 been) of a blackish or chocolate colour. The valves are 

 rather narrow across, the length of the exposed portion 

 being, for the most part, as one to five or six ; their 

 lateral areas are not well defined, but are distinguishable 

 by being rather more swollen, and generally of a more 

 opaque yellow than the central ones. The curvature of 

 the hinder edge of the plates is not considerable, and the 

 beaks are so short, as sometimes to appear obsolete ; the 

 mucro of the last valve is not at all acute, and the 

 posterior descent from it is gentle and arcuated. The 

 sculpture is so very minute as not to be distinctly per- 

 ceptible except under a powei'ful glass ; to the naked eye, 

 indeed, the surface appears glabrous. When very highly 

 magnified, however, a remarkably crowded, but depressed, 

 shagreening is observable, that, without positively being 

 irregular, is neither radiating nor transverse, but from its 

 peculiar closeness seems to occupy alike the entire super- 

 ficies. Nevertheless there is a kind of diverging arrange- 

 ment of meandering fissure-like lines near the beaks, 

 where the valves appear rather scratched and punctured, 

 than granulated ; and the quincuncial system is approached 

 upon the lateral areas. The ligamental border is only 

 moderately broad, and is adorned with large white vitre- 

 ous and almost level scales. 



Mr. Lowe remarks that the terminal valves have eleven 

 or twelve adhesional teeth, and the other plates two only 

 on each side. 



Few British specimens exceed a quarter of an inch 

 in length, and about half that breadth : foreign examples 

 are said to attain to twice these dimensions. 



