1866.] YOrNG CAEBONIFEROUS GLTPTODIPTERINES. 607 



a marginal row of short, very stout "conical teeth with fluted bases ; 

 the rest of their surface is set with similar but smaller teeth, which 

 are more distant over the anterior portion, but posteriorly pass into 

 a dense rasp of minute denticles. The connexions of these plates 

 are not seen ; but they probably fitted into the angles formed on 

 either side by the maxilla and sphenoid. Since 1861, specimens illus- 

 trating the form of the fins hare been acquired by the Museum ; but 

 the description and illustration of these parts are reserved, the pur- 

 pose of this paper being merely to give the diagnostic characters fur- 

 nished by the scales and teeth. 



The teeth are conical, more or less incurved, and of very elegant 

 proportions. Both jaws, the premaxillary region above, and the an- 

 terior part of the mandible, contain teeth larger than the numerous 

 small ones which occupy the edge of the bones, and, as in RJiomho- 

 ptycliius, form an angulated row across the roof of the mouth. The 

 surface of the majority is smooth ; many, however, are covered with 

 very fine ridges, which involve merely the outer portion of the 

 enamel, and, as Mr. Davis has pointed out to me, disappear by at- 

 trition. These lines are either parallel or anastomose to form a fine 

 reticulation ; but nothing approaching the pattern of Strepsodus, 

 either in position or symmetry, is found. In a note read before the 

 Society in February, I proposed the abolition of Centrodus, M'Coy, 

 on the ground that that tooth is avowedly a fragment, that it is unac- 

 companied by either bone or scale, and that it is identical in character 

 with teeth unmistakeably associated with Megalichthyic remains. 

 I have since had the satisfaction of finding that Mr. Davis had 

 arrived at the same opinion, a tablet of teeth from Carluke bearing, 

 as synonyms, MegaUclithys and Centrodus. 



The scales and head-bones of Megalichthys are covered by a layer 

 of smooth, porous ganoin. "When this is detached by accident, the 

 subjacent surface of bone is also smooth, but perforated by the 

 larger and smaller tubes passing up from the interspaces in the 

 osseous substance of the scale. Such is the typical appearance; 

 but in a large number of examples (fig. 6) the ganoin both of scales 

 and bones is patchy and incomplete, covering nearly the whole of the 

 surface, and only interrupted by circular spaces, which are distin- 

 guished by their concentrically sloping margins from the mucus- 

 pores, which are surrounded by a thin raised ring ; or the ganoin 

 only occurs as scattered points. A carefiilly prepared section of a 

 scale through such an isolated patch shows that, beneath the ga- 

 noin, the structure is the same as in the typical Megalichthys- 

 scale, of which Williamson has given an excellent description. The 

 ganoin ceases on either side with an abruptly rounded margin, which 

 dips down to and stops at the average surface of the scale ; for it coats 

 a low eminence made up of the kosmin or non-corpusculated bone, 

 the tufts, capillary tubes, and the upper series of Haversian canals. 

 Adjoining the patch the surface of the scale is smooth, and has, as in 

 Rhomboptychius, a close and semilustrous aspect. Under the micro- 

 scope it is seen that a thin layer of kosmin coats this part of the scale, 

 whose irregularities are formed of the upturned laminae of bone. 



