CATALOG OF THE FOSSIL FISHES IN THE CARNEGIE MUSEUM. 413 



is shown in profile, thus affording a tolerably clear idea of the arrangement of the 

 cheek and opercular plates, but yielding no information as to the covering of the 

 thoracic region; the present specimen, on the other hand, completes our knowledge 

 of the underside of the head, and displays besides the branchiostegal and opercular 

 apparatus to excellent advantage. 



The anterior portion of the space between the mandibular rami is completely 

 covered by a narrow, triangular gular plate, behind which occur the closely spaced 

 series of branchiostegal rays, these latter being in juxtaposition superiorly with 

 the angular element, interoperculum, and suboperculum in ascending order. In the 

 thoracic region the interspace between the divergent series of branchiostegal rays 

 is occupied apparently by a single, thin, delicate plate, which probably owes its 

 origin to the fusion of a number of small scales. The structure of the mandible 

 is not altogether clear, but the splenial is evidently a long delicate plate, beset with 

 small conical teeth, while the angular occupies about one-third of the outer face 

 of the ramus. The maxilla is long and slender, tapering in front, deepest behind, 

 and in its middle portion is in contact with the sclerotic ring, which is ossified. 

 The latter is apparently bounded posteriorly by a ring of small circumorbitals, the 

 boundaries between which have become obliterated. 



With regard to the structure of the fin in the type-species Agassiz remarks as 

 follows: "Les nageoires refletent en quelque sort a I'exterieur cette forme grele 

 du squelette, car leurs ra^^ons sont tous sans exception excessivement fins: Les 

 pectorales qui ont valu a I'espece son nom sont tres-developpees, fort longues, et 

 en meme temps tres-larges. Les plus grands rayons debordent beaucoup I'inser- 

 tion des ventrales. Autant les pectorales sont grandes, autant les ventrales sont 

 petites." 



These characters of the paired fins hold true for the new species under dis- 

 cussion, as well as for the type, the only difference being that the pectoral fin-rays 

 are more numerous in the present form than in S. longimanus. Upwards of forty 

 are to be counted in the specimen now in hand, and although Agassiz does not 

 state the number observed by him in S. longimanus, only half as many are shown 

 in the published illustration (Poiss. Foss., Vol. II, PI. LX). The median fins are 

 essentially alike in the two species, except for the more remote position of the 

 dorsal in the example here made the type of a new species, as already noted. The 

 caudal fin is most exquisitely preserved, and shows the upward prolongation of 

 the axis for a short distance into the superior lobe. The scales and internal skeletal 

 structure do not call for particular mention. 



