Geological Society. 259 



are more characteristically represented than in PI. X. fig. 6 

 (X30). 



Fig. 35. One of the fusiform fibres that are sometimes found lying longi- 

 tudinally upon the side of a small acerate spicule ( X 435). 



Fig. 36. Section along an incurrent canal lying in the middle of the 

 mark, showing ciliated chambers and the small outflow-tubes 

 leading towards an excurrent canal (X 140). 



Fig. 37. A very early form of globate spicule, from a preparation in 

 glycerine (X 435). 



[To be continued.] 



PROCEEDINGS OF LEARNED SOCIETIES. 



GEOLOGICAL SOCIETY. 



January 21, 1880.— Henry Clifton Sorby, Esq., LL.D., E.R.S., 

 President, in the Chair. 



The following communications were read : — 



1. " On the Genus Pleuracanthus, Agass., including the Genera 

 OrtJiacanthus, Agass. & Goldf., Diplodus, Agass., and Xenacanthus, 

 Beyr." By J. W. Davis, Esq., E.G.S. 



The author commenced with an historical account of the supposed 

 genera of fishes founded on remains occurring in Carboniferous and 

 Permian strata, mentioned in the title of his paper. The teeth 

 described by Agassiz under the name of Diplodus have been already 

 shown by Sir Philip Egerton to be associated with spines of the 

 Pleuracanihw type ; and this identification was accepted by the 

 author, who also showed that Xenacanthus, Beyrich, is identical with 

 Pleuracanthus, and that, on the ground of priority, which there is 

 no reason for disregarding, the latter name ought to be retained. 

 With regard to Orthacanthus, he indicated that in the type described 

 by Agassiz the two rows of denticles are placed close together along 

 the posterior face of the spine, while in his Pleuracanthus the 

 denticles are situated as far as possible apart on the sides of the 

 spine. In the new Carboniferous species described in the present 

 paper, and in those described and figured by the officers of the 

 United-States Survey, the denticles occupy almost every intermediate 

 position between these two extremes ; and hence the author was 

 inclined to unite Orthacanthus with Pleuracanthus. Compsacanthus, 

 Newb., is also probably nearly related to Pleuracanthus. The 

 author described in some detail the characters of the genus Pleura- 

 canthus, and discussed its scientific position, with regard to which 

 he inclined to the adoption of Dr. Rudolph Kner's opinion that the 

 Pleuracanths constitute a type of fish intermediate between the 

 Elasmobranch and Teleostean fishes, but more nearly approaching 

 the latter, probably through the Siluroids. 



