CROSSOPTERYGII. 79 



flanked on each outer margin by a single series of small square membrane- 

 bones, which have been named parafrontals. The hyomandibular and 

 pterygo-quadrate arcade are fused into a continuous triangular, lamelli- 

 fonn bone on each side, articulating with the hinder portion of the cranium 

 above, and provided postero-inferiorly with a ginglymoid condyle for the 

 articulation of the mandible below. In front of the pterygo-quadrates 

 there is a small pair of thin palatine bones with more or less formidable 

 teeth. A long slender parasphenoid bone occupies the greater part of the 

 base of the skull ending in a spatulate expansion anteriorly, where it meets 

 a large unpaired robust element, with a cluster of strong teeth, evidently 

 to be regarded as the coalesced vomers. The actual termination of the 

 snout is unknown. The eye is surrounded by a ring of small, delicate 

 sclerotic plates. The cheek behind the eye is covered by two large plates, 

 and immediately below these is another membrane-bone, named the post- 

 maxillary. A single narrow suborbital plate extends from the postorbitals 

 to the edge of the anterior portion of the cranial roof. There is a long and 

 narrow dentigerous maxilla, but the premaxilla is not certainly known. 

 The greater portion of each mandibular ramus is formed by a long, narrow 

 articulo-angular element, extended a little behind its articulation with the 

 quadrate. The small, toothless dentary meets this bone in front, reaching 

 to the symphysis, and bounded below by a thin infradentary. A long and 

 deep laminar splenial bone, tapering in front, but with a straight dentiger- 

 ous border in the greater part of its length, is apposed to the dentary and 

 articulo-angular on their inner face ; and this forms the inner wall of a 

 vacuity existing between the upper portion of the two outer elements. 

 The branchial arches are in four or five pairs, like those of Polypterus and 

 modern bony fishes ; and the copula is a single large bone, with spatulate 

 hinder extremity. There are no traces of ossifications in the sheath of the 

 notochord, but the arches are superficially ossified. The two halves of 

 each neural arch are firmly united with their appended spine ; the haemal 

 arches are delicate and rudimentary in the abdominal region, but corre- 

 spond in development with the opposed neural arches in the caudal region. 

 The long, gently curved clavicle exhibits a robust postclavicular process, 

 and its lower spatulate extremity is- overlapped by a slender infraclavicle 

 which meets its fellow of the opposite side below. The pelvic fins are 

 supported by a pair of elongated, slender basipterygia with an inwardly- 

 directed process at the distal end, by which they are loosely apposed in 

 the median line. The cartilages in the lobe of each of the paired fins are 

 unknown. Of the two dorsal fins, the anterior is destitute of baseosts, the 

 stout dermal rays articulating with the upper border of the single laminar 

 axonost. This fin therefore exhibits no lobation. The posterior dorsal fin 

 and the opposed anal resemble the paired fins in being distinctly lobate, 

 but none of the baseosts are preserved ; the axonost in each of these fins is 

 a forked bone. The caudal fin is symmetrical and supported by a single 

 series of long, slender bones above and below, equalling in number and 



