J. W.Davis — Carboniferous Fish-remains. 153 



belong to the same species, and to be the anterior tooth of P. Jonesii. 

 In this, as in others of its principal features, the species from Derby- 

 shire agrees ; and whilst in one or two minor points it is dissimilar — 

 as, for instance, in the greater expansion of the smooth posterior part 

 of the larger tooth, and the fewer number of the ridges on the small 

 one — there can be no hesitation in considering those differences as 

 not more than varietal, and including it in the same species with the 

 examples from Armagh. 



Genus Xystrodus, Agass. MS. 



Davis, Trans. Roy. Dublin Soc. n.s. vol. i. p. 447 (1883). 



Xystrodus ParJceri, Davis, sp. nov. (Figs. 3 and 4, p. 150). 



Several exquisitely beautiful little teeth have been found belong- 

 ing to this genus. They are 0-3 to 0'4 inch in length, and - 15 to 

 0-2 inch in width, sub-triangular in outline, rounded anteriorly, and 

 expanding towards the posterior margin. Surface of the crown con- 

 cavo-convex, rising on one side in the form of a ridge, depressed 

 along the opposite one, forming a broad concave channel extending 

 the whole of the length of the tooth, and expanding into a somewhat 

 aliform margin, more or less sinuous in outline. The surface is 

 enamelled, and a number of minute punctures, arranged so as to 

 form a series of sinuously parallel ridges, extend across the tooth. 



This species resembles most nearly that of Xystrodus pidchellus, 

 Davis (Trans. E. Dublin Soc. n.s. vol. i. p. 450, pi. lv. fig. 24), from 

 the Yoredale Series of Wensleydale, but may be readily distinguished 

 by its rounded anterior extremity, less acutely triangular form, and 

 the aliform character of the concave margin. The convex margin is 

 rounded in this species, in X. pidchellus it is straight. 



Xystrodus simplex, St. J. and W. (Geol. Survey of Illinois, vol. vii. 

 p. 178, pi. viii. figs. 4, 5, 1883), is a larger tooth than the one now 

 described, but is similar in form. It may be distinguished by the 

 more acute angle formed by the lateral margins and its point of 

 inrolment being more distinctly developed. The punctee on the 

 surface are without arrangement into ridges. Messrs. St. John and 

 Worthen consider that the genus Xystrodus is closely allied if not 

 identical with that of Tomodus, Agass. They remark, " While we 

 have not the data necessary for carrying the comparisons to a final 

 conclusion, we are much impressed by the intimate resemblances 

 which subsist between the present genus and Tomodus, Agass. A 

 series of careful sketches of authentic examples of Tomodus convexus, 

 Agass., from the Mountain Limestone of Bristol, England, and which 

 were kindly submitted to us by Lord Enniskillen, show this rela- 

 tionship in a striking manner. The genus Tomodus, indeed, appears 

 to be a Xystrodus in all save the arrangement of the punctae in 

 parallel transverse lines ; and in the latter respect we find a close, 

 though not absolute agreement, in the initial species occurring in the 

 American Carboniferous species X. simplex" (op. cit. p. 177). It was 

 in 1859 that the late Professor Agassiz, whilst visiting the Earl of 

 Enniskillen, took the opportunity to examine and arrange the mag- 

 nificent collection of Carboniferous Limestone fish-remains which 



