﻿STRUCTURE OF THE PALjEONISCIDjE. 



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skull of Palaoniscus are both very open to criticism. Through the great kindness of 

 Professor von Seebach, of Gottingen, I have enjoyed the opportunity of examining and 

 taking notes of the specimens referred to by Martin, and with the result of finding that 

 the author has fallen into many very serious errors of interpretation, a few of which might 

 indeed have been avoided had he been acquainted with my paper on Nematoptt/chius, 

 published six years previously. Of these errors one of the most remarkable is the finding 

 of "jugular plates," not only in Ckeirolepis, but also in Palaoniscus. It must, 

 however, be borne in mind that the subject is one of such extreme difficulty that no one 

 can with confidence imagine himself altogether free from error, and, alas ! even the best 

 preserved specimens procurable fall very far short of affording us all the information we 

 may be in quest of. 



I.— THE ANATOMICAL STRUCTURE OF THE PAL^ONISCID^. 



The Head. 



We may be very certain that the cranium in the Palceoniscida consisted internally of 

 an extensively cartilaginous box or case, in which some primordial ossifications were 

 present, and of which a few indistinct traces may occasionally be detected. Externally it 

 was covered by a buckler of osseous plates firmly united by suture, ganoid and sculptured 

 externally, which are to be considered as essentially dermal in their nature, and to be 

 classed with the numerous plates covering the cranial cartilage of the Sturgeons. We 

 need, therefore, hardly look for an exact correspondence of these plates in number 

 and arrangement with the bones forming the cranial roof in ordinary Bony Fishes, in 

 which, through the long chain of Lepidosteid and Amioid forms, these parts have under- 

 gone much modification. Some of them, however, such as the frontals and parietals, may 

 be considered as still having their exact homologues in the skulls of modern Teleostei. 



In no member of the family have I seen the elements of the cranial buckler exhibited 

 with greater clearness than in Nematoptyckius Greenoc/cii, as illustrated in PI. I, figs. 

 7 and 8, taken from a beautiful specimen, singularly free from crushing, preserved in an 

 ironstone nodule from the Lower Carboniferous shales of Wardie, near Edinburgh. The 

 specimen is, in fact, a cast of the inner surface of the bones of the head, and, as it exhibits 

 not merely the sutures between the various bones, but also the lines radiating from their 

 centres of ossification, we are enabled to map out the constituent elements with much 

 greater certainty than if the external sculptured surface of the bones themselves were 

 presented to us. The two somewhat square-shaped bones (p.) at the posterior part of 

 the shield, articulating with each other in the middle line, may be taken as representing 

 the parietals, and on the outer side of each is a somewhat longer plate (sq.), equivalent to 

 the similarly placed squamosal of Lepidosteus and Amia. In advance of the parietals the 

 frontals (/.) may be recognised, covering a large part of the vault of the cranium. 

 External to each frontal, and in advance of the squamosal, is another smaller plate [p./.), 



