J. W. DAVIS ON A BONE-BED IN THE LOWER COAL-MEASURES. 337 



on the anterior margin towards the point. From the apex to J 

 of an inch from the base the side of the spine is ornamented by lon- 

 gitudinal enamelled ridges, six in number ; the remaining portion 

 has been imbedded in the integument of the fish. The line dividing 

 the two parts lies obliquely across the spine, the posterior border 

 being the shorter one. The ridges in one or two instances, by run- 

 ning into each other, present a bifurcated appearance. The whole 

 of the spine is slightly compressed. Along the posterior margin is 

 a series of minute denticles scarcely distinguishable without the aid 

 of a magnifying-glass. 



The two genera to which these spines are most nearly allied are 

 Onchus and Homacanthus of Agassiz. They differ from the former 

 in having denticles, the genus Onchus being described by Agassiz in 

 the ' Monographic des Poissons du Vieux Ores Rouge ' as " compre- 

 hending only the Icthyodorulites w 7 hich are straight or feebly arched, 

 with longitudinal, smooth, and uniform furrow r s, and having the base 

 bevelled ;" whilst in the same monograph Homacanthus is described as 

 including very small Ichthyodorulites " armed with crenulations on 

 their posterior border, and their sides ornamented by homogeneous 

 longitudinal furrows." The only specimens known are named H. 

 arenatus " from the arched form of the spines, which are curved like a 

 sickle." The spines from the coal-measures differ from Homacanthus 

 in being straight and having the ridges bifurcating. 



Sir Philip Egerton, who has a specimen of the spine, suggests the 

 generic name " Hoplonchus " as signifying the character distinguish- 

 ing them from Onchus, which appears to be their nearest relative. 



13. Plettrodus Rankinii, Agass. 



14. Pleurodus affinis, Agass. 



I have nearly two hundred teeth of these species from the bone- 

 bed. They differ very much in form, size, and character. Some 

 have broad wing-like processes spreading from the main ridge of the 

 tooth; others are narrow and elongated. Many are ornamented 

 with a series of well-defined striae running across them transversely, 

 whilst the majority are smooth and plain or slightly punctured. 

 The size ranges from two tenths of an inch to seven tenths. Prof. 

 Agassiz named the two species, but did not describe them. Judging 

 from the manner in which the species run into each other in speci- 

 mens in my cabinet, it will probably be found, when the fish is well 

 known, that the teeth are from different parts of the mouth of one 

 species rather than belonging to separate ones. 



15. Helodus simplex, Agass. 

 Rare. Two or three teeth. 



3 6. Helodus, sp. ? 

 Rare. Tw T o teeth. 



] 7. Cladodus mirabilis, Agass. 

 JS T ot common. Teeth. 



