706 Davis — On the Fossil Fish- Remains of the Coal Measures of the British Islands. 



lateral cartilages ; ventral fins with an articulated axis supported by a pair of 

 triangular pelvic cartilages and lateral cartilages on external surface ; in the males 

 the fins are provided with claspers ; two anal fins placed one behind the other, 

 attached to the hsemapophyses by a series of intermediate ossicles. 



The genus Pleuracanthus was instituted by Agassiz* and embraced a fish spine 

 from the coal shales of Dudley ; its surface was rounded and at the same time 

 depressed and armed on each side by a range of denticles arched towards the base. 

 The spine was considered to belong to an undescribed genus of the family of the 

 Rays. One species was described, P. Icevissimus^ -A-g.")" A second species was 

 referred to six years later, but not described, viz. P. planus, Ag., in the same volume, 

 p. 177. This was from the Coal Measures in the neighbourhood of Leeds. The 

 type specimen is in the Egerton collection at the Natural History Museum, 

 London, and is now determined as the spine of a young example of P. Icevissimiis. 

 Prof. Agassiz refers on the same page J to another spine, Orthacanthus cylindricus, Ag., 

 from the Coal Measures at Leeds ; and again when considering the defences of the 

 Rays, 0. cylindricus is described as a straight spine of cylindrical form armed with 

 two rows of sharp denticles on the posterior surface. The spine is stated to be 

 from the Coal Measures in the neighbourhood of Manchester. The near relation- 

 ship of Orthacanthus with the genus Pleuracanthus is recognized. 



In 1841, Mr. E. W. Binney first noticed certain teeth from the Lancashire 

 coal field to which he appended the name Diplodus gibbosus.^ The specimen was 

 figured but without description; the latter was given by Agassiz, || and specimens 

 were described from the Coal Measures of Staffordshire and of Carluke in 

 Scotland. 



Dr. Goldfuss ^ described a specimen ascribed to the genus Orthacanthus from 

 the lower Permian Sandstones of Ruppersdorf in Bohemia exhibiting the upper 

 surface of the head and a large portion of the body. The mouth was large and 

 terminal with numerous rows of small tliree-pronged teeth. The spine, still 

 in position, was embedded in a cartilaginous mass immediately behind the head. 

 It was round, with a median ridge on the dorsal aspect ; and on each side the 

 ridge, separated by a narrow groove, was a row of denticles. The spine was 

 on front of the first dorsal fin, considered subsequently by C. Brongniart,** 

 as a cephalic fin. The second long dorsal fin was without spine. The pectoral 

 arch is described as being built up, on either side of an internal bone, composed 



* Eeoh. sur les poissons fossiles, vol. iii., p. 166. 1837. f Op. cit., pi. xlv., figs. 4 and 5. 



X Op. cit., p. 177 and p. 330, pi. xlt., figs. 7-9. 1843. 

 § Trans. Manchester Gaol. Soc, vol. i., p. 169, pi. v., figs. 17-18. 

 II Op. cit., p. 204, pi. xxn. h, figs. 1-5. 



^ Beitriigo zur vorweltliohen Fauna des Stcinkohlengebirges, p. 23, pi. v., figs. 9-11, 1847, Bonn. 

 ** Bull. .Soc. de rindustrie Minerale, ser. 3, vol. ii., 1888. 



