60 Messrs. llaneoek & Ilowse on Janassa bituminosa 



hero small aTul arranged lengthwise in parallel order, lie burled 

 in the white matter that in many instances permeates the en- 

 tire scoop ])ortion. 



The tubular matter, whether at the surface or in the interior, 

 is composed ot" concentric layers; and coarse, branched tubules, 

 originating in the medullary channels, ])enetrate their walls. 

 The whole of the brown tubular matter composing the mass of 

 the tooth is probably dentine, as we have just stated; or it may- 

 be, as stated in the paper already quoted on CUmaxodus and 

 Janassa, osteodentine, the small nuirginal tubes only being 

 dentine ; but the structure of the whole ajipears to be the 

 same. We feel equally at a loss how to denominate the 

 white matter*. It is minutely granular, but otherwise quite 

 structureless. If we are correct in desigmiting it enamel, then 

 there must be two kinds of enamel; or what is the transparent 

 film seen on the surface in perfect specimens ? 



When the white coating is worn a little, the extremities of 

 the small dentinal tubes that penetrate it are seen at the sur- 

 face ; and as they wear more readily than the white matter, 

 the whole surface becomes minutely punctured. On the cut- 

 ting-margin, however, the white matter is usually to some ex- 

 tent miiuitely grooved longitudinally, in consequence of these 

 superficial tubes of the dentine-like matter running parallel to 

 the surface. 



The minute structure of the tooth as above deserilx'd is seen 

 to be essentially the same as that of the so-called CliiiKixodus ; 

 but in the latter the brown dentinal tubular matter of the in- 

 terior is not so dense, consequently the white matter pene- 

 trates more extensively through the tissue. The small dentinal 

 tubes abutting 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. In- 

 deed 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. II. fig. 6) with whicli the body of this fish 

 is covered is exhibited in three of the four specinu^ns obtained 

 by Mr. Duff. In one of them a considerable ])atch 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 



• In the paper on Climnxodus and Janassa this white coating is called 

 "cement." On further examination, however, we find tliat it has not the 

 character of cement, but is merely granular, and in every respect is 

 similai" to the white external layer in Janassa. 



