40 WEALDEN AND PURBECK FOSSIL FISHES. 



median suture, which has sometimes one small sinuosity behind ; and their super- 

 ficial rugosity is both coarsest and strongest near the outer border, especially 

 behind, where the slime-canal traverses the bone in an L-shaped groove. The 

 squamosal (sq.) on each side is a narrower bone, extending as far forwards as the 

 parietals, but not quite so far backwards. It unites with the adjacent parietal in 

 a slightly wavy suture, and its outer face is very coarsely rugose, while the groove 

 for the transverse slime-canal behind is well marked. The squamosal is narrowest 

 in front, where it bounds the hinder end of the frontal, and meets the circum- 

 orbital ring, from which a small dermo-postfrontal is sometimes detached. The 

 frontals (PI. VIII, fig. 2 a ; PI. IX, figs. 1, 1 ^^ ; PI. X, fig. 3 ; //•.) are nearly three 

 times as long as the parietals, and unite in a very slightly wavy median suture. 

 Each is widest behind, the maximum width being about a third of the total length ; 

 and its comparatively narrow anterior portion ends in a few pointed digitations. 

 The absence of these digitations in the frontal ascribed to Lepidofvs fiftoni by 

 Agassiz (Poiss. Foss., vol. ii, pt. 1, p. 2G4, pi. xxx h, fig. 3) is due to the im- 

 perfection of the specimen. The outer margin of the bone immediately in front 

 of the squamosal is slightly indented by the overlap of the three upper plates of 

 the circumorbital ring. Its outer face is usually rugose and tuberculated only in 

 the hinder half, where the markings are coarsest near the outer margin ; it then 

 tends to rise into a rounded boss at the median suture between the orbits ; and the 

 slender anterior half is nearly smooth, only with a longitudinal channeling. The 

 nasals and other dermal bones of the ethmoid region are unknown. 



The cheek is completely covered with plates, which form a circumorbital ring 

 (PI. VIII, figs. 2, 2 a ; PI. IX, fig. 1 ; PL X, fig. 3 ; co.) bounded behind by post- 

 orbitals [po.), and continued in front by a few preorbitals (pro.). They are all 

 more or less rugose and tuberculated, but the most delicate and easily destroyed 

 markings are on the upper postorbitals. Of the circumorbital ring, three plates 

 occur above the eye, the hindmost being the largest and sometimes transversely 

 subdivided, so that a separate piece in contact with both the squamosal and the 

 frontal may be regarded as a dermo-postfrontal (e. r/. B. M. no. P. G338). The two 

 posterior circumorbitals, though of irregular shape, are about as deep as wide, 

 while the other four plates completing the ring antero-inferiorly are much deeper 

 than wide. The slime-canal is not conspicuous. There are at least four plates in 

 the preorbital series. The irregularly pentagonal upper postorbital (see especially 

 PL IX, fig. 1, po.) is comparatively large, in contact Avith the squamosal and tAvo 

 circumorbitals ; but the other plates of the postorbital series, very irregular in 

 shape, usually from five to seven in number, though sometimes further subdivided, 

 are not wider than the circumorbitals. The foremost and lowest plate' is always 

 longer than wide and tapers to a blunt point below the foremost circumorbital. 



The mandibular suspensorium is inclined forwards so that the quadrate 

 articulation is beneath the middle of the orbit. The hyomandibular (PL VIII, 



