ON JANASSA BITUMINOSA. 365 



extensively through the tissue. The small dentinal tubes abut- 

 ting at the surface, too, are more branched and are less regular. 

 The external white layer appears to be not so thick ; but it is 

 almost always so much stained with black carbonaceous matter 

 that it is not easily distinguished. Indeed we have only in one 

 instance detected it without the aid of transmitted light ; but in 

 section when so viewed its presence is usually observed. 



The shagreen (PI. X., fig. 6) with which the body of this fish 

 is covered is exhibited in three of the four specimens obtained 

 by Mr. Dufi". In one of them a considerable patch of it is very 

 beautifully displayed, no disturbance whatever having taken place 

 in the tubercles. They are minute, and, though pretty close 

 together, they are seldom in contact, there generally being a 

 space between them less than half their diameter. They are in 

 the form of irregularly rounded bosses, with the surface smooth 

 and glossy, and the margins sinuous and produced into points. 

 Sometimes, however, they are much elongated, and are fre- 

 quently very irregular in shape, with the marginal prolongations 

 much produced, variously formed, sharp or obtuse. Others 

 have one margin comparatively smooth, the points being con- 

 fined to the opposite side. Some are quite devoid of all such 

 irregularities, the margins being smooth or only a little sinuous 

 at one side : these are rounder and larger than the others (fig. 8). 

 Another form (fig. 7), not by any means uncommon, is irregu- 

 larly stellate, with the rays ridged and sometimes a little bifur- 

 cated. 



Erom the fineness of the cutting-margin in the so-called Cli- 

 viaxodus it was inferred in the former paper, so frequently re- 

 ferred to, that the food must have been composed of some soft 

 material. We are disposed to draw the same conclusion from 

 the structure of the teeth of Janassa hituminosa. The scoop-like 

 cutting-margin is certainly much used, for it is almost always 

 greatly worn in a regular manner : only in one instance have 

 we seen it a little broken. In would be an efficient instrument 

 in cutting vegetable substances, and these might afterwards re- 

 quire the aid of the crushing- disk. 



In corroboration of this view of the food we may quote a 



