﻿320 CROSSOPTERYGII. 



below the eye are conspicuous; the dentigerous maxilla bounds 

 these below, and exhibits a small (apparently jugal) plate behind its 

 posterior expansion. The latter element extends far backwards, 

 and immediately above it is a very large cheek-plate covering the 

 whole of the space between the posterior suborbitals, the cranial 

 roof, and the preoperculum. On the roof of the mouth there is a 

 well-ossified parasphenoid, meeting in front a pair of vomers, each 

 of which bears a powerful tooth ; and there are some traces of an 

 inward palatal extension both of the maxillae and premaxillae. 



The mandible is very complex and seems to possess a distinctly 

 ossified articular element. The dentary bone is relatively deep and 

 thick at the symphysis, tapering backwards, and bears a series of 

 small teeth, with a single large laniary in front. The lower 

 border is bounded by a series of three or four, plate-like, lenticular 

 bones, of which the hindermost seems to correspond to the angular, 

 while the others are conveniently termed infradentaries. A thin 

 splenial lamina forms the inner wall of the ramus, and between this 

 and the dentary is arranged a series of about three or four very 

 stout lenticular bones, each of which bears a laniary tooth. 



A deep and narrow preoperculum is observed behind the cheek- 

 plates, while the operculum and suboperculum are well developed ; 

 there is, however, no representative of an interoperculum. Below 

 the suboperculum a long narrow plate forms the hinder element of 

 the series of lateral jugulars on each side ; and a pair of very large 

 principal jugular plates, with or without a small anterior azygous 

 element, occupies the whole of the space between these series. 



The cranial roof is bordered behind by three small supratemporal 

 plates, one median and a pair lateral ; but there appear to be no 

 large scales on the posterior margin of the pectoral arch. Behind 

 this, so far as known, the squamation is always continuous; and 

 the only enlargement of the scales is observed occasionally at the 

 bases of the fins and in the anal region. There are rarely indi- 

 cations of a peg-and-socket articulation of the scales, although the 

 inner rib is usually conspicuous in those that are rhomboidal, while, 

 except in the Holoptychiidae, this rib is represented by a median boss 

 in the more deeply overlapping scales of cycloidal form. In one 

 genus (Megalichihys) the scale-arrangement proves the anus to have 

 been placed at some distance in advance of the anal fin, and not 

 quite in the mesial line. 



A lateral line arising immediately above the operculum traverses 

 a longitudinal series of scales as far as an undetermined point on the 

 caudal pedicle ; and, at least in the Holoptychiidae, there is another 

 similar line arising from the jugular plates of either side. In the 



