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



in number. The first and second have attached to them interspinous bones 

 and fin-rays. The third is larger, broad at the two extremities, slightly curved, 

 and towards the middle, on the concave side, is a sort of apophyse, to which 

 is attached an interspinous ray and a fin-ray; its extremity supports a shorter 

 and broader ossicle. The latter affords attachment to three elements — first, a 

 long and pointed ray, extending backwards, and two ossicles, of which the 

 posterior one supports . two short ossicles and fin-rays, and the anterior one 

 one ossicle and one fin-ray. " Ces nageoires anales pr^sentent done une structure 

 trfes complexe et rappellent par leur disposition de v^ritables membres."* 



Mr. A. Smith Woodward has pointed outf that the teeth of Didijmodus are 

 generically indistinguishable from those of Diplodus, and he has included the two 

 in the genus Pleur acanthus. This author is also convinced that the presence of 

 membrane bones| in the skulls of the Texas specimens is more than problematical, 

 and founded on a misconception. Reporting on a recent visit to Professor Cope's 

 collection of fish and other fossil remains at Philadelphia, Mr. "Woodward says§ the 

 skulls of the Ichthyotomous Elasmobranch "Didy modus" certainly exhibit with 

 distinctness the extraordinary fissuring of the chondro-cranium, though in the 

 strict sense of the term it is scarcely accurate to name the segmented parts 

 " bones." 



During the years 1889 and 1890 Dr. Anton Fritsch of Prague published two 

 parts of his important work on the gas coal of Bohemia,|| which are almost entirely 

 occupied with the genus Pleur acanthus^ as now defined. Dr. Fritsch prefers to 

 regard Pleur acanthus., Xenacanthus, and Orthacanthus as distinct and independent 

 genera, and bases his diagnosis upon the teeth, spines, and denticular appendages 

 of the gill arches, taken in conjunction with the construction of the archipterygium 

 and fin-rays of the pectoral fins. Four species of Orthacanthus are described, viz. 

 0. Bohemicus, Fr. ; 0. Kounoviensis, Fr. ; O.pinffuis, Fr. ; O.plicatus, Fr. ; and a fifth, 

 0. Senkenlergianus, Fr., is from Lebach. The remains are of a more or less frag- 

 mentary character. The remains of Pleuraeanthus and Xenacanthus are much 

 more perfect, and the study of them has enabled Dr. Fritsch to add considerably 

 to our knowledge of the Pleuracanths. Only one species of Xenacanthus is recog- 

 nized, the type X. Decheni, Goldf., whilst there are four species of Pleuraeanthus 

 from the Bohemian formations described, they are, P. ovalis, Fr. ; P. (Elbergensis^ 

 Fr. ; P. carinatus, Fr. ; and P. parallelus, Fr. The denticles on the sjiines of both 

 genera are lateral, but the cavity is said to be smaller in Pleuraeanthus than in 

 Xenacanthus, and there is in the former an external median groove on the posterior 



■» 



Op. cit., p. 23. t Cat. Foss. Fishes, Brit. Mus., pt. i., p. 3. 1889. 



I Op. cit., Introd., p. xxiii. § Geol. Mag. Dec, m., vol. vii. Sep., 1890. 



II Fauna der Gaskohlo und der Kalksteine der Permformation Bohmens, Baud n., Heft 4, pp. 98-112, 

 pis. Lxxii.-sc., 1889 ; and Band iii.. Heft 1, pp. 1-48, pis. xci.-cii., 1890. 



