486 Dr. A. Smith Woodivard — A Carboniferous Ichthyodondite.. 



11. — On the Carboniferous Ichthyodorulite Listracanthus. 

 By Arthur Smith "Woodward, LL.D., F.R.S., of the British Museum. 



THE problematical fish-spine, Listracanthus, has already been found 

 in the English Coal-measures; ^ but neither the specimens from 

 this country nor the earlier discoveries elsewhere are sufficient to 

 show the exact nature of the fossil, or even to determine its complete 

 form. Two groups of remains of this spine, recently discovered by 

 Mr. John Ward, F.G.S., in the Middle Coal-measures of North 

 Staffordshire, are therefore of much interest as tending towards 

 a more satisfactory knowledge of its characters. 



One of the new groups just mentioned is preserved in the middle 

 of a nodule, and probably comprises the remains of a single fish, 

 though there is no clear outline of a body. Portions of at least 

 70 spines of Listracanthus are scattered through the fossil in an 

 entirely irregular manner, and they are mingled only w^ith smaller 

 dermal tubercles, without any indication of bones or cartilage. So 

 far as they can be observed, all the spines appear to be nearly 

 similar in size and shape, and their principal features are indicated 

 by the fragments represented in the accompanying Figs. 1-3. 

 A generalised restored sketch of a complete spine is given in 

 Fig. 4. They are all encrusted with a very thin film of pyrites, 

 and their dark brown substance (presumably vasodentine) is so 

 brittle that it is usually more or less flaked when uncovered by the 

 hammer. Each spine is a thin, solid lamina, which seems to be 

 bilaterally symmetrical, tapers a little towards the apex, and is 

 slightly arched either backwards or forwards. The straight base- 

 line is oblique with respect to the long axis of the spine, and its 

 extent equals about one-fifth of the total height. Each lateral face 

 is flat and marked by nearly parallel, vertical ridges, which are 

 twelve to fourteen in number at the base, and are gradually reduced 

 by terminating in succession at the sharp anterior and posterior 

 borders. At the concave border the upper end of each ridge is 

 produced into a short, straight, pointed denticle; and the interval 

 between every two denticles thus formed is occupied by a similar 

 point arising independently. Fewer ridges terminate at the convex 

 border, which seems to have been quite smooth and regular, without 

 denticles except near the apex, where they are few and incon- 

 spicuous. The apex is not pointed, but comprises a little cluster 

 of sharp denticles, which are partly formed by the ends of the 

 lateral ridges, partly independent and intercalated. The ridges 

 are very delicate and sharp throughout, quite smooth, of uniform 

 thickness, and separated by comparatively wide, smooth interspaces. 

 As shown by a transverse section of the spine (Fig. 5), the ridges 

 of the two faces are usually not opposite, but alternating. The 

 ornament terminates very close to the base-line, so that the inserted 

 portion of the spine is insignificant, and it is scarcely expanded. 



^ H. Bolton, "On the Occurrence of the genus Listracanthus in the English 

 Coal-measures": Geol. Mag., Dec. IV, Vol. Ill (1896), pp. 424-^23, mth 

 Fiffure. 



