FOSSIL AND RECENT 119 



unlike the latter is vertical. The dorsal margin of the lateral face of the ectoptery- 

 goid is produced as a small crest. The teeth borne by the ectopterygoid and endo- 

 pterygoid form a single large patch. Unlike those in 0. lewesiensis, the teeth in this 

 patch vary considerably in size and shape. Those situated medially resemble the 

 larger parasphenoid teeth. Those found laterally are similar to the villiform teeth 

 seen in the type-species. The anterior end of the hyopalatine series is not known. 



Mandible. The mandible is short, turned inwards markedly at the symphysis 

 and with a posteriorly situated coronoid process. Ventrally the dentary is marked 

 by a deep groove which runs parallel to the inflected margin, and carried the sensory 

 canal. Posteriorly the mandibular sensory canal ran through the articular. The 

 oral surface of the dentary bears a broad band of teeth. Each tooth is pointed and 

 curves inwards distally like those of 0. levis but unlike the villiform teeth of 0. 

 lewesiensis. The articulatory facet is formed mainly by the endosteal articular 

 which is relatively larger than that element in the type-species. 



Circumorbital series. The anterior half of the first and the third, fourth and fifth 

 infraorbitals are the only elements of this series known. Unlike those of the type- 

 species, all bones are thin and marked only by growth lines. The first infraorbital 

 shows a rounded anterior margin and is without the small dorsal prominence seen in 

 0. lewesiensis. The surface of the first infraorbital is marked by concentric growth 

 lines and in the dorsal half there is a thin ledge which protected the sensory canal. 

 The third, fourth and fifth infraorbitals form the posterior border of the orbit. These 

 elements are narrower than those of 0. lewesiensis, leaving more of the cheek region 

 exposed. 



Hyoid arch and branchiostegal rays. Both anterior and posterior ceratohyals are 

 short and deep, contrasting with those of the type-species. The posterior ceratohyal 

 carried five branchiostegals and at least six are attached to the anterior ceratohyal. 

 All branchiostegals are smooth but otherwise they resemble those of 0. lewesiensis. 



Cephalic sensory canal system. The sensory canal system is more open than in 

 0. lewesiensis. The supraorbital canal ran within the frontal from the level of the 

 autosphenotic to open onto the surface of the frontal at the level of the lateral 

 ethmoid. Anterior to this the canal must have lain in the frontal trough. The 

 infraorbital sensory canal of 0. latifrons is relatively larger than that of 0. lewesiensis 

 and, unlike that of the latter species, is situated at the orbital margin. Within the 

 third infraorbital the canal opens to the surface by large pores, separated from one 

 another by narrow bony struts. On the first infraorbital the canal must have been 

 open ventrally, the only protection being afforded by a narrow ledge of bone. The 

 mandibular sensory canal was similarly open, lying as it did in a large groove. The 

 only point at which the canal passes through bone is at the extreme postero-ventral 

 angle of the articular. The preopercular sensory canal ran within an intramural 

 canal in the dorsal half of the preoperculum. At the level of the fourth infraorbital 

 the canal emerged to the surface and continued its path beneath a narrow shelf. 



Opercular series. The preoperculum is large and reaches well forward. The dorsal 

 end of this element is narrow and truncated. Anteriorly the bone is rounded. The 

 operculum differs in shape from that of the type-species. The anterior margin is 

 almost straight while the posterior border curves backwards and downwards to near 



