80 WHITE AVES ON" FOSSIL FISHES FEOM 



second dorsal fins are imperfect. The bony supports of these fins and about five inches 

 of the vertebral column are beautifully preserved and well exposed in another specimen. 

 The only parts of the head found so far are fragments of the jaw, with teeth, and some 

 isolated cranial plates, one of which is evidently the operculum. 



" In associating this species with the name of its discoverer, the writer desires to 

 acknowledge his obligation to Mr. A. H. Foord for valuable assistance in the study of 

 the various specimens described in this paper." 



The paper from which the foregoing description is quoted is dated March 31st, 1881, 

 but in the summer of that year quite a number of additional specimens of Eusthenopteron 

 were collected by Mr. Foord, which atford much new information both in regard to its 

 external characters and interior structure. 



In the American Naturalist for February, 1883, a brief summary of some of the new 

 features exhibited in these specimens was published and it was there stated that the 

 caudal fin of Eusthenopteron is not heterocercal, as was at first supposed, but that its rays 

 are divided into three pointed lobes, as in Tristiclwpterus, and attention was called to its 

 close resemblance to that genus in many other respects. No attempt, however, was then 

 made, or has since been made, to give as detailed a description of the present genus or 

 species as the material now in the museum of the Survey would admit, a deficiency 

 which the present paper is intended to supply. 



The most instructive specimens collected by Mr. Foord ,in 1881 are six in number, 

 whose state of preservation may be thus described : — 



No. 1. — This, which so far as the organism itself is concerned is the largest specimen 

 known to the writer, is about two feet long and consists of the head and part of the 

 body of an apparently adult individual, which, when entire, must have been upwards of 

 three feet in length. In this specimen, the greater part of which is represented on 

 Plate VII, the fish has been crushed nearly flat from above downwards, in a direction at 

 nearly a right angle to the normal lateral compression. Most of the cranial buckler is 

 well preserved, as are also the facial bones of one side of the head, though these latter are 

 much distorted, and some are disi^laced in such a way as to overlap or partially overlap 

 one another, while others have their margins much broken. The two large pectorals are 

 well exposed in place, and parts of the first dorsal and of one of the ventrals are preserved. 

 By removing the matrix from the under sirrface of the head, a considerable portion of the 

 lower jaw and one of the large jugulars have also been exposed. In this specimen, the 

 stout interspinous bone whose expanded outer extremity or apophysis supports the three 

 osselets to which the fin rays of the first dorsal are articulated, exceeds an inch and a 

 half in length. 



No. 2. — This consists of a slab of stone about three feet, four inches in length and 

 fourteen inches in its greatest breadth, one of whose surfaces is strewn with detached 

 and isolated bones or dermal plates of the head, scales or small clusters of scales, and 

 parts of the bony supports of the fins of a large individual. The unbroken outlines of 

 the two large jugailar plates and the exact shape of the suboperculum are well shewn in 

 this specimen, as is also the whole of the under surface of the lower jaw. 



No. 3. — A fragment shewing the under surface of most of the right side of the head 

 of another large individual, in which several of the actual sutures can be clearly traced. 

 The exact outlines of the right maxillary, of two of the suborbitals, of the suboperculum 



