372 Messrs. Hancock & Atthey on Reptile- and Fish-Remains 



size. The largest are three-quarters of an inch from the base 

 to the apex of the large or lateral spines ; the smallest, mea- 

 sm-ed in the same way, are not more than one-twelfth of an 

 inch in extent. Between the two extremes, tubercles of every 

 size occur. Now the smaller individuals, which are by far 

 the most numerous, agree very well with Diplodus minutiis 

 of Agassiz, so far as the imperfect specimens described and 

 figm-ed by that author permit a comparison. M. Agassiz says 

 he was not able to discern the median cone ; but this is not 

 to be wondered at, for none of his figures represents the base 

 entire. 



Note. — Dittodus divergens^ Aganodus apicalis^ Aganodus 

 undatus, Pternodus jproductus^ and Ochlodus crassus, described 

 in the paper " On the new Coal Fishlets," are all referable to 

 Diplodus. The genus Dittodus is established on two very 

 dissimilar fossils : D. parallelus is, we have already seen, 

 founded on the fragment of a jaw with a few of the teeth of 

 Rhizodopsis sauroides / Dittodus divergens (pi. 2) is apparently 

 nothing more than Diplodus minutus * of Agassiz \ and, like his 

 figure, that given by Prof. Owen is represented without the 

 small central spine : indeed it is scarcely possible to show 

 it in such a section as that figured in plate 2. The size, 

 form, and histological characters all agree with those of our 

 sections of the minute specimens of Diplodus. 



Pter nodus productus (pi. 10) is the single-spined variety of 

 Diplodus gihhosus seen in profile, with a well-produced base ; 

 or it may possibly be a lateral section of a fully developed 

 specimen in which one of the large spines only is exhibited. 

 In either case the same appearance would be presented of the 

 large projecting " heel," with its outline sweeping into the 

 curve of the spine ; and, in fact, the form, proportions, and 

 size all exactly agree with those of similar sections in our 

 possession of the single-spined variety of Diplodus. The mi- 

 nute structure is precisely the same ; the greater portion, how- 

 ever, of the basal marginal boundary, from m to J in fig. 1, 

 pi. 10, has been ground away ; and that which is designated 

 ^^ osseous tissue of jaw " is merely a portion of the osteo-den- 

 tine of the pulp-cavity. 



There are two species of Aganodus described : one, A. api~ 

 calis (pi. 9), is based apparently on a section made from before 

 backwards of a single straight spine of the small variety of 

 Diplodus. The two processes (o) below the spine are project- 

 ing portions of the base, the most of the base itself having 

 been broken away. The opening between the two processes 

 ♦ Poissons Fossiles, vol. iii. p. 205, tab. 22, f. 6-8. 



