From the Coal- Measures. 325 



Genus VI. — Aganodus, Owen, (a, priv. fyayo?, shine, o^ov^, tooth). 



Species 1. — Aganodus apicalis, Owen. 



This genus seems characterised by the absence of the enveloping 

 layer of enamel observable in Ganolodus, etc., and there is also a 

 different disposition of the dentinal tubules. 



Species 2. — Aganodus undatus, Owen. 



The form and structure of this tooth differs from that of Ag. 

 apicalis in a degree which induced the author to present it under 

 a distinct specific name. 



Genus "VII. — Pternodus, Owen {rrrepva, heel, 68ov<;, tooth). 



Species 1. — Pternodus productus, Owen. 



Some of the small teeth, with crowns of unvascular dentine 

 uncoated by ganoine, have the hinder part of the base drawn out 

 like a heel ; they differ from the type Aganodi in a more gradiaal 

 basal expanse of the pulp -cavity, and in the absence of the thin 

 platform of hard osteodentine which supports in them the crown 

 of the tooth, and divides it from the ordinary bone of the jaw. 



Genus Vin. — Sagenodus, Owen (a-dyijvr), seine, 68ov<i, tooth). 



Species 1. — Sagenodus inequalis, Owen. 



The teeth of this genus offer a type of structure akin to the extinct 

 Dictyodus and the existing Splitjraena, appearing as tooth-like pro- 

 cesses of the jaw, of which they continue the structure with little 

 modification. 



Genus IX. — Characodus {yapae, a pointed stake, 6hov<i, tooth). 



Species 1. — CJiaracodus confertus, Owen. 



The teeth of this genus are of the Dictyodont type of structure. 



Genus X. — OcModus, Owen (o;^A,o9, crowd, 6Sov<i, tooth). 



Specie 1. — OcModus crassus, Owen. 



Close set as are the teeth in parts of the dental series of the last- 

 mentioned genus, they are more crowded in the fragment of the 

 alveolar part of a jaw of this genus for which the author proposes 

 the name OcModus crassus. 



Genus XI. — Oreodus, Owen, {opevi, mule, 6Sov<;, tooth). 



Species 1. — Oreodus rohustus, Owen. 



(Probably a species of Aganodus, allied to A. undatus). 



Genus XII. — Gastrodus, Owen (^acTTT^p, belly, 0801/9, tooth). 



Species 1. — Gastrodus prcBpositus, Owen. 



Of this genus there have been discovered two portions of denti- 

 gerous jaw and of detached teeth. All the most complete teeth 

 show a large pulp -cavity, inclosed by a thin wall of unvascular 

 dentine, and in no case does any tissue, like osteodentine, encroach 

 upon the pulp-cavity. In this respect the teeth resemble those of 

 Dendrerpeton, and the Frog, and differ from the teeth of most Fishes. 



The tissue of the dentine, as well as that of the jaw-bone, bears 

 the same resemblance to those in the BatracMa cited. 



After carefully and minutely describing the details of the struc- 

 ture of this genus. Professor Owen infers that we have in Gastrodus 

 evidence of a minute air-breathing Batrachian, of the age of the 

 lower Coal-measures of Northumberland. 



