326 J. w. DAYis oiq- the genus pletjeacanthtjs, agass. 



siderable stress on the presence of a large groove or channel extend- 

 ing along the inferior face of the spine. In the several specimens in 

 my own cabinet from the Lower and Middle Coal-measures of York- 

 shire, there is no evidence of such a groove ; the anterior and pos- 

 terior faces are, as nearly as possible, one the counterpart of the other. 

 The upper part of the spine was strong, the internal cavity very 

 small ; and the specimens remain un crushed. The lower part of the 

 spine was thinner, and the cavity proportionally larger, the result 

 being that the walls of the base are frequently crushed together and 

 broken. It appears probable, judging from the figure of Plevra- 

 cantJms in the ' Poissons Fossiles,' that the basal portion of the spine 

 was crushed in this manner, and misled M. Agassiz into supposing 

 that there was a deep groove extending along the spine. Examples 

 from the Staffordshire Coal-field, probably from the same stratum from 

 which M. Agassiz's specimen was obtained, fail to exhibit any traces- 

 of this groove. 



Locality. L. CM. near Halifax, and M. CM. at Tingley. 



2. Pleueacanthtts eeectus, sp. nov. Fig. 2. 



Sjoine straight, 3'5 inches long, "4 inch wide at the p j~^ 2, 



base, converging in straight lines to an acute point. , 

 Oval in section ; the transverse diameter one third -^^^'^^«c«^^/^f S" 

 greater than that between the posterior and anterior ^^^^ ^*' ^^^®* 

 faces. An internal canal traverses the spine nearly its 

 whole length ; near the base it is oval in form, and the 

 walls are thin and crushed ; thence the cavity contracts 

 and becomes circular, occupying the centre of spine. 

 Externally the anterior and posterior rounded faces 

 are covered with longitudinal striations ; and a number 

 of small pittings are studded indiscriminately over the 

 surface, sometimes on the ridges, at others in the fur- 

 rows. At the junction of the anterior and posterior 

 faces the lateral edges are produced, and form a series 

 of blunt compressed projections or denticles. They 

 extend fully three fourths the length of the spine, and 

 are from 22 to 24 in number on each side ; they are orna- 

 mented similarly to the general mass of the spine. 



Locality, Cannel Coal, Tingley (M. CM.). 

 - P. erectus is a particularly straight example of the 

 genus ; and from this character I have ventured to 

 derive its specific name. In general form it is some- 

 what similar to P. Icevissimus, Ag. ; but it is different 

 in almost all the details. It is more elegant-looking, 

 and converges from the base straight to the point on ; 



all sides. Its denticulation in no way resembles that of 

 P. Icevissimus, excepting in its lateral arrangement. 

 The teeth are broad at the base, widely separated, and \ 



very blunt-pointed ; in P. Icevissimus ihej aie closely '^'^ '■ 

 set, long, and acuminate ; the spine is less than half Spine, nat, 

 the size of that of the latter species. size. 



