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PROCEEDINGS OF THE OEOLOGICAL SOCIETY. [Feb. 21, 



Amphicenteum, nov. gen. PI. XX. 



Body flat, broad, prolonged into peaks, a dorsal and ventral pro- 

 tected by indurated scales : the depth of the trunk thus exceeds its 

 length. The prolongation into the upper caudal lobe is short, and 

 tapers rapidly. Head triangular, nearly equilateral. Premaxilla 

 very large, edentulous. Maxillae and mandibles very strong: the 

 opposed surface of each presents two ridges, on which are inserted 

 dental plates raised into distant tubercles ; their substance is tra- 

 versed by large medullary canals, which reach the surface of the 

 tooth, terminatiug there in fine pores. The palato-vomerine area is 

 occupied by a pair of plates bearing, each, three longitudinal rows of 

 alternating dental tubercles like those of the jaws. Branchiostegal 

 rays few, enamelled, not projecting below mandible, covered by an 

 interopercular. No ventral fin : dorsal opposite, and longer than 

 anal. Tail heterocercal, equilobate. Scales oblong, ornamented, like 

 head-bones, with tubercles. Lepidopleura very strong, terminating 

 inferiorly in modified marginal tubercles; notochord persistent, arches 

 well ossified. 



A. GRANULOSUM, Huxlcy. 



This genus is founded on a large number of specimens, all from 

 the North Staffordshire Coalfield. 



The general arrangement of the head-bones (fig. 1) resembles that 

 of Platysomus, the distinctions in detail are. however, well marked. 

 The occipital crest is bounded by two parietals. The frontal is very 

 broad : the anterior and posterior frontals are massive, and project 

 well over the orbit. Behind the latter, separating it from the pari- 

 etal, is a strong plate {Sq.), the true squamosal, giving attachment 

 to the suspensorium. The posterior frontal thus receives only the 

 hinder end of the suborbital arch. The frontal and anterior frontal, 

 are both received on the broad end of the hour-glass bone (Eth.) 

 which abuts against the premaxillae, a pair of massive elongated 

 edentulous bones forming a strong beak : its outer surface is tuber- 

 culate above, but near the tip covered with compact and smooth 

 ganoin. The nasals are thrust out laterally, and applied against the 

 ethmoid, the nasal apertures being completed externally by a plate 

 from the suborbital ring, which is analogous to a lachrymal in many 

 Teleosteans. The vertical upper portion of the maxillary (PI. XX. 

 fig. 2) bulges below into an abruptly projecting labial mass, whose 

 oral margin forms a ridge separated by a shallow groove from an 

 inner ridge. Seen from below, this groove terminates sharply behind 

 by the approximation of the outer and inner ridges : but is closed in 

 front by the premaxilla. On the outer ridge the dental tubercles 

 are few : on the inner, which is more prominent, they are more 

 numerous, less so however than on the mandible (PI. XX. fig. 4.), 

 which is the converse of the maxilla, in that the ridges approximate 

 in front (the tubercles ceasing before their coalescence), while the 

 groove is open posteriorly: the outer ridge is also the more prominent. 



To the naked eye, and even under the lens, no line can be detected 

 between the substance of the tubercles and that of the jaw. Under 



