84 MESSBS. HANCOCK AND ATTHEY ON 



All tliese bones, as well as several other fragmentary speci- 

 mens, have the surface covered more or less densely with strong 

 vermicular sculpture composed of hollows and ridges ; the latter 

 in some become tubercular, but in others stream over the sur- 

 face smoothly and regularly, with here and there an occasional 

 bifurcation ; in others, again, the vermicular grooves are intri- 

 cately involved, and sometimes they are broken up to form 

 circular pits. These are the dominant markings in the bones 

 already before us ; but the sculpturing on the surface of some 

 opercular plates which we also assign to the same large fish, and 

 which wUl presently be described, is somewhat modified. In 

 these the vermicular ornament is less developed, and the pitted 

 and tubercular predominate, the ridges being rough and much 

 broken up. 



It is on account of these peculiar surface characters that we 

 deem these bones to belong to Rhizodus ; but this is not the only 

 evidence. On the slab, with the anterior jugular plate, there is 

 a portion of a scale of Rhizodus ; and on that with the two large 

 jugulars several scales of this fish are found lying in contact with 

 them. If we are right in attributing these scales to Rhizodus, 

 we have in the above facts strong corroborative evidence that 

 these bones also belong to it. 



The opercular plates above referred to are four in number: 

 three are opercles, one is apparently a prseoperculum. They are 

 all crescentic in form, having their anterior margins well hol- 

 lowed, and both extremities considerably produced. The largest 

 operculum is six inches from point to point, and is upwards of 

 2|- inches wide ; the posterior margin is a little sinuous, and is 

 bordered with several parallel depressed lines, probably indicative 

 of growth ; the anterior margin is bounded by a wide, smooth, 

 articular surface, which is divided from the rest of the operculum 

 by a ridge. The prasoperculum is similar in form to the opercu- 

 lum, but it is wider in proportion to its length, and there is a 

 single groove following the sinuosities of the posterior border, the 

 anterior margin is concave, with a very narrow articular surface. 



Note. — It is the intention in this and the following notes to 



