/. — Pleuracanthidce. 739 



extending over 0'13m.: on each margin of the Pleuracanthus erectus there are 

 only forty-five denticles, and they occupy exactly the same area as the others. 



The example last referred to has a length of 0'22 m. ; at a distance of 0'07 from 

 the basal extremity the lateral diameter of the spine is 0"012 m., and thence it 

 gradually diminishes to an attenuated point at the distal end, and towards the 

 base the diameter is also reduced. The spine is oval in section, compressed antero- 

 posteriorly ; its walls are comparatively thin at the basal end. The internal pulp 

 cavity appears to have been terminal. 



A spine of P. erectus, having a length of 0*21 m., has been found in the shale 

 immediately above the two-feet coal at Bardsley. Other specimens, not so 

 perfectly preserved, have been found, and associated with them examples of 

 P. Icevissimus, Ag. The denticulated margin of the specimen first referred to 

 occupies O'll m., rather more than one-half the length of the spine ; the number 

 of denticles is thirty-one on each side. A comparison of the more or less 

 fragmentary spines of the two species exhibits very clearly the difference in 

 denticulation which has been observed in those from other localities. 



Formation and Locality. — Cannel Coal, Middle Coal Measures, Tingley ; 

 Lowmain Coal Seam, Newsham ; Two-feet Coal Seam, Bardsley. 



Ex coll. — James W. Davis, Halifax ; Museum of Natural History Society, 

 Newcastle-on-Tyne ; Greorge Wild, Bardsley. 



Pleuracanthus horridulus, Traquair. 

 (PI. Lxxii., figs. 22, 23.) 



Pleuracanthus horridulus, . Traquair, R. H., 1882, " Greol. Mag.," ser. ii., 



vol. ix., p. 541. 

 Pleuracanthus horridulus, . Woodward, A. S., 1889, " Cat. Foss. Fishes Brit. 



Mus.," pt. I., p. 9. 

 Pleuracanthus horridulus, . Woodward & Sherborn, 1890, " Cat. Brit. Foss. 



Verteb.," p. 154. 



Length of spine, 1 inch ; diameter at base, -^ inch ; gently arched, tapering 

 to a point, lower part striated, upper smooth ; upper third of posterior surface set 

 with a double row of large recurved denticles, eight or nine on each side, placed 

 alternately with each other. 



The specimens referred to were described by Dr. Traquair without figures, 

 and I have not the originals for reference ; other specimens of this species from 



