﻿POSITION OF THE PAL-EONISCID.E. 



41 



but concerning which 1 may at present express my conviction that they must accompany 

 the Palao viscid a wherever the latter are placed. 



The genera Eurynotus, Jlesolepis, Eurysomus, Platysomus, Atnphicentrum, and 

 Wardichthys, though differing most remarkably among themselves in the form of their 

 dental apparatus, nevertheless, in general structural characters, form a well-marked 

 group or " Formen-Reihe." They are closely allied to the Palaoniscida in their com- 

 pletely heterocercal tail ; in the structure of their fins, which are fulcrated, composed 

 of numerous closely set rays, exceeding in number their supporting ossicles, and whose 

 lateral halves or demi-rays imbricate in the fore part of the fin ; the dorsal is also sup- 

 ported by two sets of interspinous bones. The opercular bones and branchiostegal rays 

 are constructed on exactly the same type as in the Palaoniscida, though the mouth is 

 smaller, from the more vertical direction of the hyomandibular, which in Platysomus 

 slopes even a little forwards. The shoulder-girdle is like that in the Palceoniscida, and 

 possesses infraclavicular. The bones of the cranial roof are very like those of Palceo- 

 niscus, at least posteriorly, those about the snout (which does not project over the mouth) 

 seem to differ a little, though here our information is not sufficiently perfect. The scales 

 of Eurynotus are similarly shaped with those of the Palaoniscida, so is its anal fin, 

 though the dorsal has already assumed the peculiar extended contour characteristic of its 

 more immediate allies. The peculiar shape of the scales of the other genera, which are 

 high and narrow, and have their internal rib and articular spine of unusual strength, and 

 coincident with the anterior margin, does not seem to me to be a character of prime 

 importance. I cannot, therefore, agree with Professor Young in associating the Platy- 

 somid fishes in one " sub-order " with the Pycnodonts, with which they have nothing in 

 common save the deep form of the body, the persistence of the notochord, and the mode 

 of articulation of the scales — the latter being a character which does not hold in 

 Eurynotus, and is also found in the Lepidosteid Tetragonohpis. I shall pursue this 

 subject further in a future part of the present work ; meanwhile, however, I feel convinced 

 that the sub-order of " Lepidopleuridse " must be abandoned, that the Platysomida must 

 accompany the Palaoniscidce, and that the position of the Pycnodonts, or even whether 

 they are Ganoids at all, as doubted by Professor Huxley, has yet to be determined. 



According to the views here expressed the position of the Palao/iiscida would 

 be as below : 



Order Ganoidei. 



Sub-order I. Dipnoi. 



II. Crossopterygii. 

 III. Acipenseroidei (see p. S). 



Family 1. Acijoenserida. 

 2. Spatularida. 



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