1853,] EGERTON PALICHTHYOLOGIC NOTES. 279 



the outer surface of the scales. A second specimen shows the inner 

 surface with their characteristic articulations. The general form and 

 outline of the fish correspond more closely with Tetragonolepis cy- 

 closomus than with any other species of the genus. It differs from 

 that species in the smaller diameter of that portion of the flank 

 below the vertebral column, as compared with the dorsal portion, or 

 that above the line of vertebrae ; it also differs from that and the other 

 species in the arrangement and relative proportions of the scales. 

 The head is small and its profile semicircular ; the opercular flap is 

 singularly restricted in dimension, while the lower jaw and the bran- 

 chiostegous apparatus are no less singularly expanded ; the operculum 

 and suboperculum are both remarkably small, bu.t the interoperculum 

 is comparatively large ; the jaws are thick and broad, and furnished 

 with an outer row of elongated conical teeth ; the masticatory appa- 

 ratus of the interior of the mouth is not seen ; the lower jaw is 

 especially remarkable for its great depth, so m^uch so, that it resembles 

 an oval plate rather than a member of the maxillary series ; the 

 angle between the lower jaws is closed by a pair of broad plates re- 

 ferable to the hyoid systemj and these are succeeded on each side by 

 a pair of expanded branchiostegous rays. Immediately behind and 

 below the thoracic arch is a single strong carinated scale with a ser- 

 rated keel, being the first of a series extending along the ventral 

 margin as far as the commencement of the caudal fin. The vertebral 

 column, as indicated by the elevation of the scales along its course, is 

 straight ; the scales in the row immediately above it are perforated for 

 the transmission of the mucous secretion. Above the lateral line are six 

 or seven rows of small rhomboidal scales, obliquely arranged and in- 

 creasing in depth as they recede from the back. The number of scales 

 in each series below the lateral line varies from five to six, the scales 

 of the second and third rows being the largest ; in those containing 

 six rows the last scale is the smallest, but in those having only five, 

 the scales vary little in dimensions ; they are all coated with a layer 

 of highly lustrous ganoine, having a slightly eroded character when 

 examined through a lens: the margins are entire. The fins are unfor- 

 tunately deficient in all the specimens, but the base of the pectoral 

 fin is traceable in a higher position than is common in the Pyaio- 

 dontidce, it being nearly coincident with the union of the operculum 

 with the suboperculum. We are indebted to the zealous researches 

 of the Rev. P. B, Brodie for this interesting addition to our British 

 Fossil fishes, who discovered it in the beds of the Upper Lias at 

 Dumbleton in Gloucestershire. 



DESCRIPTION OF PLATE XI. 



Fig. 1. Teeth of Dapedius, magnified. 



Fig. 2. Teeth of Dapedius punctatus. 



Fig. 3. Scales of Tetragonolepis sxibserraius, inner view, magnified. 



Fig. 4. Teeth of Tetragonolepis droserus, magnified. 



Fig. 5, Tetragonolepis discus. 



