J. W. DAVIS ON ANODONTACANTHTJS. 



427 



33. On Anodontacaxthtts, a new Genus of Fossil Fishes from the 

 Coal-measures ; with Descriptions of three new Species. By 

 James W. Davis, F.G.S. &c. (Eead May 11, 1881.) 



[Plate XXIX] 



The spines which form the subjects of the following descriptions 

 are from the West-Riding Coalfield in Yorkshire, and the Ironstone 

 occurring in the Lower Limestone series near Edinburgh. A strati- 

 graphical description of the Cannel Coal at Tingley, from which the 

 first two species have been obtained, may be consulted in the 

 Quarterly Journal of the Geological Society issued for February 

 1880, page 56. 



The three species of Ichthyodorulites forming the subject of this 

 paper are the only specimens of which I have cognizance possessing 

 their peculiar characteristics. In some particulars they resemble 

 the genus Pleuracanthus ; they are composed of a strong, close- 

 grained, fibrous substance. Their general form is also similar to 

 that of the Pleuracanths : the internal cavity is terminal at the basal 

 extremity ; and the walls become thinner near the base in comparison 

 with the remainder of the spine ; the method of implantation in the 

 body of the fish must also have been the same. The great distin- 

 guishing feature between the two rests in the absence in this genus 

 of any form of denticulation. In the Pleuracanths there are two 

 rows of denticles either along each lateral surface or on some portion 

 between the lateral and posterior lines. Whether this may be a 

 sufficient distinction to necessitate a second genus, or further dis- 

 coveries will prove that it must be included in the genus Pleura- 

 canthus, remains to be seen ; but for the present it may be better 

 to consider it as a distinct genus, for the following reason : hitherto 

 remains of the fish Pleuracanthus, where found in even tolerable 

 perfection, as in the Stone-coal of Bohemia, have always had associ- 

 ated together the three-pronged teeth of the so-called Diplodus, and 

 a spine, the latter more or less straight, but always possessing, in one 

 situation or another, two rows of denticles. From Tingley, where the 

 spines under discussion have been obtained, I have several slabs of 

 Cannel Coal covered with a mass of cartilage full of the mosaic-like, 

 minute, rhomboidal, bony centres characteristic of Pleuracanthus, 

 with numbers of teeth, and occasionally a spine in situ ; but in all 

 cases the spine has been denticulated. So far all the evidence goes 

 to show that the spines of Pleuracanthus were armed or ornamented 

 by these denticular appendages ; there is a possibility, however, that 

 a specimen may be found with a spine without denticles in association 

 with undoubted Pleuracanthus-Tema.ms ; and should that happen, it 

 will be necessary to modify the character of the genus so as embrace 

 this one. Until such evidence is forthcoming, it may be regarded as a 

 distinct genus, for which the name Anodontacanthus may not be in- 

 appropriate, signifying a toothless spine. 



