FOSSIL FISHES. 35 



CHONDBOSTEID^E (? ). 

 Genus ASTEEOSTEUS (nov. gen.)- 



Of this fish tlie cranium only is known, arid of this all the specimens 

 yet obtained are incomplete. The head was apparently long and narrow, 

 tlie sides nearly straight, broadening suddenly in the occipital region. 

 The posterior margin of the cranium shows two broad arches — one on 

 either side, of the median line — in which the cranial bones are deeply ex- 

 cavated, as though for muscular attachment. The skull is terminated be- 

 hind by two conspicuous rounded projections having the aspect of con- 

 dyles, but which, so far as can be seen, show no articulating faces. The 

 iipper surface of the cranium is covered with relatively large, beautifully 

 stellate tubercles, which vary considerably in size. Toward the nasal ex- 

 tremity are two linear furrows which diverge from the middle line of the 

 cranium, and inclose two strongly-marked elliptical pits that closely re- 

 semble the nostrils of some reptiles. In none of the specimens of this 

 peculiar fish yet obtained, have the outlines of the cranial plates been dis- 

 tinguishable ; the surface being covered by a sheet of tubercxilated enamel 

 by which the sutures are entirely concealed. On the sides, the cranium 

 is somewhat beveled off, as though for the attachment of some coria- 

 ceous or ligamentous appendage, or perhaps for co-adaptation to lateral head 

 plates ; none of which have, however, been found. The dentition of Af^- 

 terosteus is quite unknown, as no jaws or teeth have been discovered with 

 its remains. 



The figure given on Plate LIV. will show better than a description the 

 general aspect of this singular cranium, and there are certain features 

 which it reveals, that will strike the most casual observer. These are the 

 condyle-like posterior projections of the skull, and the strongly marked 

 nasal pits. Until more material shall be accumulated for determining its 

 structure and relations, it would be presumptuous to make any comparisons 

 between this fish and other known living or fossil forms, but the reptilian 

 aspect of the cranium will not fail to be noticed by all who shall see the 

 figure now published. So far as yet known no reptiles existed in the 

 Devonian age, and the reptilian features presented by Asterosteus are per- 

 haps merely superficial resemblances, but there is little doubt .that if 

 found in rocks of a later date, this would be considered (until proof to the 

 contrary were gathered) the cranium of a reptile or amphibian. Though 

 a number of crania of Asterosteus have been obtained in the Corniferous 

 limestone of Ohio, none of them show either jaws or teeth, and it is quite 



