Osteology o/'Caturas and Oiteorachis. 387 



supramaxilla ; s.o., suborbitals; scl., sclerotic; sp.o., supra- 

 orbitals ; sq., squamosal ; t., bony tesserae ; x, dermal bone on 

 ethmoid. 



Plate IX. 



Figs. 1, 1 a. Catunts, sp. ; suspensorium, mandibular, and byoid arches, 

 outer and inner aspect, two thirds nat. size. — Oxford Clay ; 

 Peterborough. [B. M. no. P. 6901.] 



Fig. 2. Hypohyal of same specimen. 



Fig. 3. Gular plate of same specimen, imperfect behind. 



Figs. 4, 4 a. I^asal bones of same specimen, outer and inner aspects. 



Figs. 5, 5 a, 5 b, Cciturus, sp. ; hypocentrum, anterior, lateral, and inferior 

 aspects, nat. size. — Ibid. 



ag., angular ; ar., articulation of mandible ; c.hg., ceratohyal ; c.n., circum- 

 orbital ; ror., coronoid ; (^., dentary ; ec/j^., ectopterygoid ; enpt., 

 entopterygoid ; ep.hij.^ epihyal ; g.r., gill-rakers; hni., hyoman- 

 dibular ; l.f., lower articular facette ; p., process of hyouian- 

 dibular for operculum ; p-op., preoperculum ; qu., quadrate ; 

 upL, splenial. 



Plate X. 



Figs. 1, 1 a. Osteorachis Leedsi, sp. n. ; hinder portion of cranium 

 superior and hiferior aspects, two tifths nat. size. — Oxford, 

 Clay ; Peterborough. [B. M. no. P. 8388.] 



/;•., frontal; /^.c, hypocentrum ; n., neural arch; op.o., opisthotic; p.t., 

 post-temporal ; /<«., parietal; pl.c, pleurocentrum ; jl;?-.o., pro- 

 otic ; pt.f., postfrontal ; s., interorbital septum ; sq., squamosal. 



Plate XI. 



Fig. 1. Osteorachis Leedsi, sp. n. ; hyomandibular of type specimen, inner 



aspect, two hfths nat. size. /., foramen ; p., process for support 



of operculum. 

 Fig. 2. Right maxilla of same specimen, outer aspect, two fifths nat size. 



.r, bone-fragment. 

 Figs. 3, 3 a. Portion of left mandibular ramus of same specimen, outer 



and oral aspects, two fifths nat. size, d., dentary ; spl., splenial. 

 Figs. 4, 4 a, 4 b. Pleurocentrum of same specimen, anterior, superior, and 



lateral aspects, two thirds nat. size, not., surface for notochord ; 



n.a., facette for neural arch. 

 Figs. 6, o a, b b. Hypocentrum of same specimen, anterior, inferior, and 



lateral aspects, two thirds nat. size, tut., surface for notochord ; 



tr., trans\ er.^e process ; .r, depre:?sion ; g, bony prominence. 

 Figs. 6, 6 a. Bight half of neural arch of same specimen, anterior and 



exterun-lateral aspects, two thirds nat. size, the left half restored 



in outline in fig. 6. a, median articulation ; c, lacettes fur 



pleurocentra ; n.c., neural caual ; p., prominence. 



The numbers in square brarkets refer to the Register of the Department 

 of Geology in the British Museum, where the original specimens are 

 preserved. 



