334 J. W. DAVIS ox THE GEIfTJS PLEUEACANTETJS, AGASS. 



mation of the rows of denticles is now proved not to be a feature of 

 such importance as to render a distinct genus necessary ; indeed 

 the frequent occurrence of the denticles of P. cylindricus widely 

 separated renders this feature of little value. Taken in conjunction 

 with the fact that nearly all the species of Orthacantkus described 

 since 0. cylindricus have been more or less curved, there can be no 

 reason why the genus should not merge in Pleur acanthus. 



10. Pleueacanthus Waedi, sp. nov. PL XII. fig. 6. 



Imioerfect s^nne, 6 inches long, base and point wanting ; broadest 

 part -5 inch, and the opposite end -3 inch in diameter. It is curved 

 backwards. The anterior surface is semicircular in section, and 

 covered with very fine longitudinal striae. The sides are produced 

 somewhat squarely ; posterior portion, from the median lateral angle 

 to the point of insertion of the denticles, is depressed, as in fig. 9. 



Pig. 9. — Pleur acantlms Warcli, Davis. 



Section of spine, nat. size. 



There are two rows of denticles, extending along 4 inches of the 

 posterior face of the spine in this specimen. In a perfect example 

 the extent of denticulated surface would considerably exceed this 

 length. The rows of teeth are about one tenth of an inch apart, 

 and are separated by a median groove ; they are obtusely pointed ; 

 the intervening spaces are connected together so as to form a con- 

 tinuous longitudinal ridge, produced from the surface of the spine, 

 rather than a series of separate teeth. The internal cavity is large 

 in proportion to the size of the spine. 



This species is distinguished from P. cyliuclricus, the species to 

 which it is most closely allied in form and characteristics, by its 

 decidedly curved form, by the arrangement of the denticular lines 

 so as to form a continuous ridge with slight obtuse projections, and 

 by the narrower space constituting a simple groove between them. 

 I have much pleasure in employing the name of Mr. Ward, of 

 Longton, in order to distinguish this spine specifically. Like most 

 workers in fossil ichthyology, I have been much indebted on many 

 occasions to his uniform kindness and willingness to render assistance, 

 either by his extensive knowledge or the ample contents of his 

 cabinets. 



Locality. New Ironstone (Eagmine), Penton, Staffordshire. 



11. Pleueacanthtjs den-tictjlatus, sp. nov. PI. XII. fig. 7. 



Spine. Length 2-2 inches, diameter -2 of an inch ; basal end not 

 perfect. From the base it becomes gradually smaller, and ends in a 

 fine point. It is slightly curved dorsally. The anterior and lateral 



