PAL.EONISCTJS, GYEOLEPIS, AND PYGOPTERITS. 557 



how far its structure agrees with that of the original type of the 

 genus, and have even sometimes overlooked distinctions of more than 

 generic importance. 



The species of Palceoniscus enumerated and described by Agassiz in 

 the ' Poissons Fossiles ' are referable to at least seven different types. 



I. Type of Palceoniscus Freieslebeni, Ag. (Genus Palceoniscus 

 restricted). The body is elegantly fusiform ; the scales moderate, 

 sculptured ; the fins of comparatively small size ; the dorsal situated 

 opposite the interval between the ventrals and the anal ; the rays of 

 the pectoral are articulated ; the fin-fulcra are small but easily 

 recognizable. The suspensorium is very oblique, the operculum 

 and interoperculum broad ; the mandible is slender. The teeth are 

 small, conical, sharp, and of different sizes, the smaller ones being 

 more externally placed, but without specially prominent laniaries. 

 The species here included are Palceoniscus Freieslebeni, magnus, 

 rna&ropoqms, elegans, co)nptus, longissimus, and macroplithalmus. 

 Palceoniscus, if limited to the species just enumerated, becomes 

 intelligible as a genus ; otherwise it seems to me, as already stated 

 in the preliminary part of this paper, that the conception of a 

 Palceoniscus becomes so vague that no tangible ground of distinction 

 can be found between it and Amhlypterus and many other genera 

 of the family. It is most closely allied to Eloniehtliys ; but from 

 that genus it is distinguished b} T the small size of the fins, and by the 

 dentition, in which the differentiation of " laniaries " has not pro- 

 ceeded so far. The teeth, however, are not " en brosse," as 

 described by Agassiz, though their small size sufficiently accounts 

 for his use of the term ; probably, also, they were not very perfectly 

 exhibited in the specimens then at his disposal ; indeed in those 

 from the German Kupferschiefer they are rarely seen at all. 

 Agassiz's description of them as being " en brosse," and also " si 

 excessivement petites qu'il est tres-rare de pouvoir les distingrier "*, 

 has been rather severely criticized by Messrs. Hancock and Atthcy ; 

 it must, however, be borne in mind that the species (Egertoni) in 

 which they correctly described the teeth as being " disposed in two 

 distinct rows, one within the other, much in the same fashion as in 

 Megalichthys and Rliizodopsis, but still much more like that which 

 obtains in Pygopterus, in which the teeth are likewise arranged in 

 two rows — one being of large laniary teeth, the other of small 

 external ones," is not a true Palceoniscus, but is more properly 

 referable to Eloniehtliys. The passage referred to was also 

 written \)\ Agassiz in special reference to the species occurring in 

 Continental Permian strata, and before he became acquainted with 

 those Carboniferous forms with conspicuous laniaries which he 

 somewhat incorrectly referred to the same genus. 



As above restricted, the genus Paleoniscus must meanwhile be 

 considered as limited to the Permian formation, though it has 

 hitherto been looked upon as common also to the subjacent Car- 

 boniferous rocks. It will presently be seen that the so-called 



* Poissons Fossiles, vol. ii. pi. 1. 



