l62 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



Genus ANODONTACANTHUS J. W. Davis. 

 Quart. Journ. Geol. Soc, xxxvii, 1881, p. 427. 



A genus of ichthyodorulites represented in the Coal Measures of 

 England and in the Permian of Bohemia and Texas. It may be defined 

 as follows: 



Revised description oj genus: 



1. Spines straight, or very gently arched, as viewed from the side. 



2. No denticles along posterior margin. 



3. Lateral faces ornamented either with incised lines which are 



discrete for some distance and then anastomose or end 

 abruptly; or with lines and pittings arranged so as to give 

 a reticulated appearance. 



4. Pulp-cavity circular in cross-section, completely inclosed, large 



(occupying about one-third the width of the cross-section 

 in the proximal part of the spine) and gradually diminishing 

 in diameter distalward. 



In 1881, J. W. Davis described (50 <2) three species of Carboniferous fish- 

 spines, two from Yorkshire and one from near Edinburgh, for which he 

 proposed the generic name Anodontacanthus. They differed from all other 

 ichthyodorulites in the absence of denticles along the posterior margin; 

 but in several respects they were suggestive of the head-spines of Pleura- 

 canthus, enough so, in fact, to raise the question whether Anodontacanthus 

 might not really be identical with this genus. 



In 1888, Traquair showed that one of these three species — the one 

 from Scotland, Anodontacanthus fastigiatus — ^was a weathered Pleuracanth 

 spine. In a large series of these spines he found that some "are smooth and 

 without denticles, others show, in all stages of apparent wearing away, 

 undoubted stumps of denticles, whereby the species fastigiatus falls into 

 Pleuracanthus " (66 a) . The removal of one of the three species of Anodonta- 

 canthus to Pleuracanthus did not, of course, invalidate Anodontacanthus, 

 which should still be retained as a provisional genus. . 



In 1889, Fritsch in his "Fauna der Gaskohle," page 113, plate 86, 

 fig. 5, described and figured a similar spine from the Permian of Bohemia, 

 to which he gave the name Platyacanthus ventricosus. This spine falls 

 within the definition of Anodontacanthus and hence Platyacanthus must be 

 regarded as a synonym. 



The genus is represented in the Permian of Texas by a distinct species 

 which is described below. 



Anodontacanthus americanus n. sp. (Plate 26, figs. 5-5J.) 



Type: A spine lacking both distal and proximal extremities. Length 

 of preserved portion, 59 mm. Diameter at widest part, 10 mm. No. 7934 

 Amer. Mus. Red Beds, Texas. 



This species is distinguishable from the Bohemian one, A. ventricosus 

 (Fritsch), by its smaller size, the shape of its cross-section and the absence 

 of pittings in the striatlons. The American form is stouter and not such an 

 elongated ellipse in cross-section (the character which had apparently sug- 

 gested the generic name Platyacanthus to Fritsch). From the two Carbonif- 

 erous species it is distinguished by its cross-section and by the details of 

 ornamentation. 



