348 Messrs. Hancock & Atthey on Beptile- and Fish-Remains 



the mandibular rami. In Rhizodus^ however, there appear to 

 be two other plates, as we have already seen : these would lie, 

 pne on each side of the median line, immediately behind the 

 anterior plate, which is very nearly as wide as the two others 

 put together. 



All these 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 surface smoothly and regularly, with here and there an 

 occasional bifurcation ; in others, again, the vermicular grooves 

 are intricately 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 will presently be described, is somewhat modi- 

 fied. In these the vermicular ornament is less developed, and 

 the pitted and tubercular predominate, the ridges being rough 

 and much broken uj). 



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 prjeoperculum. They 

 are all crescentic in form, having their anterior margins well 

 hollowed, and both extremities considerably produced. The 

 largest operculum is six inches from point to point, and is up- 

 wards of two and a half 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 proBoperculum 

 is similar in form to the operculum, but it is wider in propor- 

 tion to its length, and there is a single groove following the. 

 sinuosities of the posterior border ; the anterior margin is con- 

 cave, with a very narrow articular surface. 



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

 comment on the value of the various genera and species re- 

 cently proposed by Prof. Owen in his paper " On the Dental 

 Characters of Genera and Species, chiefly of Fishes, from the 



