Remarks on the Genus Megalichthys (Agassiz), etc. 71 



opportunity of examining the specimen in question, and 

 though I find that on one side there is in the position in- 

 dicated a triangular space formed by a displacement of the 

 adjacent cheek-plates, I fail to see how it can be interpreted 

 as an orbit, while, on the other hand, the position of the 

 real orbit can, I think, be readily enough recognised in the 

 place where we would expect to find it. 



3. I have not seen in any specimen of Megalichthys the 

 foramen which occurs between the frontal bones in Osteolepis 

 and Diplopterus. 



4. Although omitted in Miller's and Pander's figures, 

 lateral jugular plates are undoubtedly present in Osteolepis 

 and Diijlopterus, as well as in Megalichthys. 



The microscopic structure of the teeth of the Old Eed 

 Sandstone Saurodipterines is not yet fully elucidated ; so far, 

 however, as external shape goes, there is nothing of sufficient 

 importance to exclude Megalichthys from the grouj). 



Then as regards the fins. The Saurodipterini have 

 obtusely lobate pectoral and ventral fins, two narrow dorsals, 

 one similarly shaped anal, and a caudal which may be 

 heterocercal {Osteolepis) or diphy cereal {Bi'ploiptcTus) , Tri- 

 plopterits of M'Coy, supposed by him to have only one dorsal 

 fin, is a genus which is really non-existent, as it was founded 

 on a specimen of Osteolepis, compressed in such a manner as 

 to show both ventral fins, one of which was mistaken for the 

 single dorsal. The dorsal fins vary in position in Osteolepis 

 and Diplopterus, being in the latter opposite the ventrals and 

 anal res]3ectively, while in Osteolepis, the first dorsal is in 

 advance of the ventrals, and the second opposite the space 

 between the ventrals and the anal. Now we have already 

 seen that the lobate form of the pectoral in Megalichthys 

 Hihlerti was not unknown ; it is noticed by Mr Ward,^ and was 

 indeed incidentally alluded to long before by Agassiz ^ him- 

 self in describing what he supposed to be the ventral fin of 

 Glyptolepis, but which was in reality a portion of the 

 pectoral.^ A specimen from the coal-measures of Dalkeith, 

 in the Edinburgh Museum of Science and Art, shows also very 



^ Loc. cit. 2 Poissons Fossiles du vieux Gres rouge, p. 63. 



' Pander, op. cit., p. 68 ; Huxley, o/p. city p. 7. 



