I. — Pleuracanthidce. 729 



produced an impure coal, locally termed " hubb." The fisli-remains are found 

 indiscriminately in the pure cannel and the hubb, and associated with them are 

 myriads of Unios and fresh-water shells. The latter probably served as food for 

 the Pleuracanths, whilst the Coelacanths, which also existed in very large numbers, 

 were probably vegetable feeders. Large spines of Ctenacanthus and Gyracanthus are 

 not uncommon, and there can be no doubt that these sharks existed in the same 

 lagoons and preyed on the smaller fish : the strong, sharply-pointed barbs with 

 their lateral recurved rows of booklets of the Pleuracanths would serve as an 

 admirable defence against their more powerful adversaries. 



A peculiar and abnormal specimen of P. Icevissimus was found by Mr. George 

 Wild, of Bardsley, in the shale forming the roof of the coal at the Arley Mine, 

 Burnley. The specimen is imperfect. The part preserved is 0-105 m. in length, 

 and consists of the middle part of a spine. The base and the point are wanting ; 

 the spine is oval in section, and denticles extend along each lateral margin as in 

 the typical examples of the species. This one differs, however, from the types in 

 several particulars. On one side of the spine there are three rows of denticles 

 instead of one (PI. lxxii., fig. 4), and on the opposite side there are two rows in one 

 part of its length, whilst on the remainder there is only a single row. The latter 

 margin is free from denticles for a distance of 0-045 m. from the basal end; whilst the 

 margin with three rows extends the whole length of the existing part of the spine. 

 In the shorter row there are twenty-one denticles on the median lateral line, 

 and from the fourth to the tenth denticle the row is double (fig. 5). The denticles 

 are strong and broad at the base; the apex curved backwards; and a groove 

 extends along their base parallel with the length of the spine. There are thirty- 

 three denticles in the median row on the opposite side, flanked on the one side by 

 thirty-two denticles, smaller but of similar form, and on the other by twenty -three 

 denticles extending from the basal end, but disappearing towards the distal ex- 

 tremity. The structure of the spine has the same dense character possessed by 

 others of this species, and in other respects it is similar. The presence of the extra 

 rows of denticles is apparently only an abnormal aberration from the type. 



M. Brongniart* states that the small spine of Pleiiracanthus pulchellus, Davis, 



from the cannel coal of Tingley is very nearly related to the spine of Pleura- 



canthus Gaudryi, Brong., from the Upper Coal Measures of Commentry in France ; 



and the spine figured and described by Dr. Fritsch f as Pleiiracanthus ovalis 



does not appear to differ in any essential respects. It is similar in size to 



P. elegans, Traq., and P. piilchellus, Davis ; it has about twenty denticles on 



each side, and in other respects resembles the spines of immature examples of 



P. Icevissimus, Ag. 



* ]i^tudes sur le terrain houiller de Commentry, Fauna Ichthyologique, pt. i., p. 33. 1888. 

 f Pauna der Gaskohle Bokmens, vol. iii., pt. i., p. 13, pi. xci., figs. 9, 10. 



5 2 



