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



Leeds, and was doubtless from the same locality as those mentioned above, and 

 with them, may be included in this species. 



The specimens described by Dr. R. H. Traquair* as Pleuracanthus elegans bear 

 a close resemblance to the small spines from Tingley, originally described as a 

 separate species but now included in Pleuracanthus Icevissinms. The form, size, 

 and number of lateral denticles is almost identical with the Tingley specimens, 

 and if the latter are the young examples of this species, there can be little difficulty 

 in assigning the small spine described by Dr. Traquair to this species also. The 

 type is described as two and a-half inches in length, from the Blackband Ironstone 

 of Borough Lee, near Edinburgh, and in the collection of R. Kidston, Esq., of 

 Stirling. 



The spines of Pleuracanthus Icevissimus, Ag., from the cannel coal at Tingley 

 are almost cylindrical in section as compared with those from the Fenton and 

 Longton localities in Staffordshire. The latter are compressed antero-posteriorly, 

 and oval in section ; the sjjines from the Lowmain Seam near Newcastle are 

 similar to those from Staffordshire. The lateral denticles on the Yorkshire 

 specimens are larger and more widely separated than those of the other localities 

 named (see PI. lxxii., fig. 3). The number of denticles on the spines from the 

 several localities offers considerable variety. The specimens found at Tingley, at 

 Fenton, and the one from Newsham, represented by fig. 6 have between fifty-five 

 and sixty denticles on each side, whilst the specimen, fig. 7, from the same 

 locality, has only thirty-two, and the one from Shattleston, fig. 8, near Glasgow, 

 has forty on each margin. The smallest examples, about two inches in length, 

 average about eighteen or twenty on each side. Presuming that all these specimens 

 are of one species, it would apjDear that the number of denticles increases with the 

 age and size of the spine. 



The occurrence of a large number of species represented by an abundance of 

 specimens of each in the cannel coal of the West Riding of Yorkshire f appears to 

 indicate that Pleuracanthus flourished and attained its greatest numerical develop- 

 ment in fresh water. The cannel coal extends over a considerable area, in patches 

 two or three miles in diameter, thickest in the centre and thinning off towards the 

 edges, proving that it was accumulated in a series of lakes or lagoon-like dejKes- 

 sions. The coal is a very pure carbonaceous substance with only 2 or 3 per cent, 

 of earthy matter, and attains a maximum thickness of about two feet. To accu- 

 mulate this large mass from the gradual decay of the leaves and spores shed by 

 the plants growing in or about the lagoons would take a long time, and indicates 

 a period of great quiet. Occasionally a stream ran through the lagoons bearing 

 fine mud, and the latter settled along with the vegetable matter, and together 



* Geol. Mag., ser. ii., vol. viii., p. 36. f Quart. Journ. Geol. Soc, vol. sxvi., p. 56. 



