ESPECIALLY MYCTOPHOIDS 83 
considerably longer than the rest of the teeth although of the same form. The 
remainder of the teeth decrease in size posteriorly. 
The articular forms the posterior mandibular region, and contains the concave, 
transversely orientated articular facet. There is a small retroarticular process 
behind the condyle which bears a deep groove passing around the condylar facet. 
This groove extends forwards ventro-laterally along the articular and dentary, and 
housed the mandibular sensory canal. The anterior and dorsal regions of the 
articular are in the form of a thin sheet of bone inserted on to the internal face of the 
dentary. 
Ornamentation on the mandible is sparse ; a few longitudinal ridges occur at the 
ventral angle of the jaw radiating forwards and upwards on the articular. From the 
symphysial end of the dentary several ridges run backwards and downwards. The 
most prominent ridges are ventro-lateral in position. 
ADDENDUM. A small very imperfect neurocranium from the English Chalk was 
also prepared in acid, B.M.N.H. number P.6461 (Text-figs. 37, 38B). This specimen 
had been noticed by Woodward (1901 : 193 and 1903 : 58) and included by him in 
the species Enchodus lewesiensis. This specimen would clearly seem to represent a 
species of Enchodus but there are several features which differ from those already 
noticed in the description of Enchodus lewesiensis. However since so little of the 
neurocranium is preserved and nothing of the remainder of the body, the erection of 
a new species is unnecessary. It will suffice here to point out the differences that 
are apparent. 
Comparing the dorsal neurocranial views (Text-figs. 32 and 37), the differences in 
the relative proportions of the roofing bones are obvious. The actual cranial cavity 
is more elongated in P.6461 than in 4001 (the specimen used in the description of 
Enchodus lewesiensis). In fact the whole neurocranium would appear to have been 
longer and narrower in P.6461. The post-temporal fossae are similar in both speci- 
mens but the dilatator fossa of P.6461 is larger and clearly visible dorsally (as it is in 
Enchodus fawast ; Goody, 1968, fig. 1). In 4oo1 the dilatator fossa faces laterally 
and is hardly visible from the dorsal aspect. The epiotic of P.6461 is more pro- 
nounced and backwardly projecting, and lateral to it, at the rear end of the post- 
temporal fossa, the fenestra entering the neurocranium below the fossa is larger 
than in 4001. 
The most interesting difference between the two concerns the trigemino-facialis 
chamber in the prootic. This complex has been considered in some detail by 
Patterson (1964 : 434) where he deals with the changes that have occurred in the 
chamber during the evolution of the acanthopterygians. In P.6461 (Text-fig. 38B) 
the pars jugularis has three openings to the exterior. An anterior one in the hind 
face of the orbit, a posterior one opening on the lateral face of the prootic and a third 
one opening midway between the anterior and posterior openings. This last 
mentioned opening is large and the wall of the pars jugularis posterior to it is reduced 
to a narrow splint of bone. This opening would have transmitted the hyomandibular 
branch of the facial nerve dorsally, and presumably the orbital artery entered 
ventrally (the facial foramen leading into the pars ganglionaris in the medial wall of 
