SKULL DIPNOI 



117 



Lepidosiren and widest in Ceratodus, usually regarded as a fronto- 

 parietal; it usually extends almost to the posterior end of the cranium. 

 In Ceratodus this frontoparietal is bounded on either side by a bone 

 called both supraorbital and dermal ectethmoid, which extends from 

 the nasal nearly to (Ceratodus) or beyond the hinder end of the skull 

 (Lepidosiren). In the latter genus these supraorbitals overlap the 

 sides of the frontoparietals; in Protopterus they meet in front, dorsal 

 to that bone. Ceratodus has a 'squamosal' articulated by its whole 



Fig. 123. Fig. 124. 



Fig. 123. — Dorsal armor of Dinichlhys iniermedius (Hussakoff, '05). Dotted lines, 

 lateral line canals; cranium and trunk armor separated, adl, anterior dorsolateral; c, 

 central; dm, dorso-median; eo, external occipital; m, marginal; mo, median occipital; 

 p, pineal; pdl, posterior dorsolateral; po, plo, pre- ajid postorbital; r, rostral. 



Fig. 124. — Dorsal side of head of Coccosteus (Traquair from Woodward '98). 

 Left gives the usual interpretation of parts, right that of Biitschli; dotted lines position 

 of lateral line organs, adl, anterior dorsolateral; al, anterior lateral; c, central; civ, 

 clavicle; do, dermoccipital; e, ethmoid; eo, exoccipital; /, frontal; Ipl, lateral plate; m, 

 marginal; md, median; mx, maxilla; n, naris; nu, nuchal; op, operculum; or, orbit; 

 p, parietal; pel, postclavicle; pdl, posterior dorsolateral; pi, pineal; pi, posterior lateral; 

 pm, premaxilla; po, preorbital; psf, postfrontal; so, supraclavicle; sq, squamosal. 



length to the supraorbital, in Lepidosiren by a narrow process; in 

 Protopterus it is separated by a considerable interval, and in all three 

 it extends ventrally over the outer surface of the quadrate. Cerato- 

 dus has a postorbital in front of the squamosal, the first of a series of 

 lateral hne bones, extending forwards (suborbitals) beneath the eye. 

 These do not occur in the other genera. 



