58 FOSSII, FISHES OF THE ENGLISH CHALK. 



nearly all the other fragments ascribed to it by Agassiz are doubtless correctly 

 determined. There seems, however, to be doubt about the small jaw figured 

 loc. cif., pi. xxv c, fig. 7, which is probably an imperfect dentary of Tomognathus ; 

 also perhaps about the two palatine bones, figured upside down loc. cit., pi. xxv c, 

 figs. 9, 10, which are imperfectly preserved and may belong to another species of 

 Enchodus. 



The skull is associated with the typical form of mandible in several known 

 specimens, and is well displayed both in the original of PL XIV, fig. 1, and in a 

 smaller specimen in the British Museum (no. P. 5415) already figured in Proc. 

 Geol. Assoc, vol. x, pi. i, fig. 5. There is also an isolated imperfect cranium in 

 the Beckles Collection (B. M. no. P. 6461) evidently of the same form. The 

 maximum depth of the head seems to have been nearly equal to its length ; and it 

 is much laterally compressed. The cranium closely resembles that of Oimolichthys, 

 but is more laterally compressed and deeper in its hinder part. The small supra- 

 occipital bears the usual posterior crest (PI. XIV, fig. In, socc. ; also seen in B. M. 

 no. 4071) ; and the epiotics form the narrow, unornamented, upper rim of the 

 occiput. The parietals are diminutive, but seem to have just entered the orna- 

 mented part of the cranial roof, as in Halec (PI. XIII, fig. 4, pa.). The ordinary 

 radiating ridges on the frontal region (/r.) are very finely tuberculated, those 

 radiating over the postorbital region being fewest and most sparse, those directed 

 outwards over the supraorbital flange the finest and most crowded. The median 

 frontal depression is deep ; and its flattened floor, both in the original of PI. XIV, 

 fig. 1, and in another small specimen (B. M. no. P. 5415), is marked with low 

 tubercles arranged along the radiating lines of growth of the bones. The meseth- 

 moid must have been very short, but it has not hitherto been observed. 



The orbit is relatively larger than that of Eurypliolis boissieri (Text-fig. 12, 

 p. 56) and must have been completely bordered behind and below with a narrow 

 ring of circumorbital plates. One of the hinder plates is partly shown in PI. XIV, 

 fig. 1, co. It is deeper than broad, traversed by a large vertical slime-canal, and 

 ornamented with radiating rows of tubercles. Part of one of the lower plates 

 remains in B. M. no. P. 5415, exhibiting traces of a similarly large slime-canal, 

 with a tuberculated upper rim and a serrated lower edge. The antorbital (ao.) 

 is shown in the same specimens. Its deepest portion in front is marked with a few 

 tliiu but prominent ridges, all finely tuberculated, which radiate downwards from a 

 point situated antero-superiorly. Its hinder portion forms a long and narrow 

 extension beneath the orbit. Its lower border is crimped and serrated. 



The mandibular suspensoriuin is vertical, so that the quadrate articulation is 

 directly beneath the occiput. In one specimen figured by Agassi/ (loc. cif., fig. 2), 

 the quadrate exhibits its posterior notch for the reception of a small symplectic. The 

 metapterygoid (mpt.) is a relatively large and thin, nearly triangular lamina, The 

 entopterygoid (PL XIV, figs. 1, 2, enpt.) is also a very thin lamina, so transparent 



