Heviews — Dr. A. Fn'tsch — Palceozoic Fishes. 377 



Bpecimens. The characters of the teeth, dorsal spine, of the denticles 

 upon the branchial arches, and of the pectoral fins, are quoted as 

 diagnostic ; while of Pleuracantlivs and Xenacantlms the materials 

 suffice to justify the two restorations reproduced through, the courtesy 

 of Dr. Fritsch, on the opposite page. 



As in Britain, Orthocanthis is only known in Bohemia from com- 

 paratively fragmentary remains. To it are referred (i.) rounded 

 spines having posteriorly placed denticles; (ii.) large teeth with a 

 relatively small median denticle ; (iii.) clustered branchial tubercles ; 

 and (iv.) long pointed pectoral fins without horny fin-rays. Four 

 Bohemian Permian species are determined, and a fifth (0. senhen- 

 hergianus) is briefly described from the corresponding horizon of 

 Lebach. Even yet, however, the genus is far from being satisfactorily 

 diagnosed ; and with reference to the dentition, we venture to think 

 that it would not be difficult to cite more than one British specimen 

 proving the occurrence in one and the same mouth of the two forms 

 of teeth which Dr. Fritsch regards as characteristic of Orthacanthus 

 and Plenracanthiis respectively. 



Some brief remarks on three undetermined Ichthyodorulites follow 

 the account of Orthacanthus, and bear the newly-applied generic 

 names of Tubulacanthus, Brachtacanthus, and Tlaty acanthus. These 

 names may be only provisional, but we would remark that the first 

 is an inadmissible hybrid, while the two latter are pre-occupied. 



The sections devoted to Pleuracanthus and Xenacanthus, with the 

 general conclusions resulting from the study of these types, make 

 a most important advance in our knowledge of the group to which 

 they belong. As will be observed in the author's restored figures 

 of the two genera (Figs. 1, 2), Pleuracanthus is a somewhat more 

 slender fish than Xenacanthus, and differs considerably in the 

 character of the fins ; in the former genus there are no dermal 

 skeletal parts and the pectoral fin is much elongated, whereas in 

 the latter genus dermal fin-rays are conspicuous and the pectoral 

 is comparatively short and broad. The cavity in the dorsal spine 

 is also described as relatively smaller in Pleuracanthus than in 

 Xenacanthus. Four Bohemian species of the former genus are 

 determined, and short notes follow on the German P. sessilis and 

 the French P. Gaudryi ; while of Xenacanthus the type-species 

 X. Decheni is regarded as the sole known representative. Numerous 

 detailed descriptions with beautiful figures of various parts of the 

 skeleton appear in connection with the several species ; and the 

 systematic work concludes with a chapter of general observations 

 on the organization of the Pleuracanth fishes as now known. 



The results are briefly summarized in the following statement : 

 The skin in these fishes was destitute of scales ; the cartilaginous 

 skeleton exhibits everywhere a granular calcification ; the skull 

 consists of a continuous piece of cartilage, without investing 

 membrane bones ; the nuchal spine is fixed upon a papilla of the 

 cranial roof, and is not connected with a fin ; the axial skeleton of 

 the trunk is notochordal, with a calcification of the central fibres ; 

 the neural arches are strongly developed, and in two genera there 



