|:M FOSSIL FISHES OF THE ENGLISH CHALK. 



Description of Specimens. — The type specimen in the Brighton Museum (Willett 

 Collection, no. 61) comprises the head with the anterior part of the abdominal 

 region of a large fish, much fractured and crushed, exhibiting part of the 

 pectoral tin on the left side and part of the dorsal fin behind. The right side 

 of the head is represented in PI. XXVIII, fig. 2, an upper view of the ethmoidal 

 region is given in fig. 2 a, and separate drawings of the left premaxilla and 

 imperfect dentary are given in figs. 2 b and 2 c. There are more fragmentary 

 specimens in the British Museum, two of these exhibiting a considerable portion 

 of the trunk. There is also a specimen in the collection of Mr. Henry C. Drake, 

 F.G.S., of Hull. 



The superficial bones show no ornamentation, merely the lines of growth, and 

 in places sensory canals. The cranial roof (so far as it can be examined in the 

 type specimen and in B. M. no. P. 10218) appears to resemble that of Pacliyrhizodus 

 (Text-fig. 30), both in general contour and in the separation of the parietals by a 

 small supraoccipital bone. The mesethmoid (PI. XXVIII, fig. 2 a, eth.) is short 

 and broad, truncated in front. The cheek is completely covered with thin bony 

 plates, which are for the most part smooth and never tuberculated. There are 

 three postorbitals (fig. 2, po.), which are marked only by inconspicuous radiating 

 grooves and by the usual slime-canal, from which a few branches radiate back- 

 wards (B. M. no. P. 10320). The lowest postorbital, which is the largest, meets a 

 long and narrow suborbital plate (so.), which rapidly tapers at each end and is 

 only marked on the middle of its smooth outer face by a few ridges radiating 

 apparently from the traversing slime-canal. The antorbital must have been small, 

 but is unknown. 



The mandibular suspensorium is nearly vertical, so that the quadrate articula- 

 tion is beneath the occiput. The premaxilla (fig. 2, pmx.; fig. 2 b) is relatively 

 small, elongate-triangular in shape, and does not meet its fellow of the opposite 

 side in the median line, the wide mesethmoid intervening. On its oral margin the 

 bone bears a single regular series of very stout, small, conical teeth, which are 

 sometimes slightly inclined backwards and inwards. Within this outer row the 

 premaxilla also bears one or two comparatively large, smooth, conical teeth. In 

 the type specimen (fig. 2 b) the anterior inner tooth, shown only by the base, is the 

 smaller of the two ; while the well-preserved, posterior inner tooth occurs at about 

 the middle of the bone. Both are somewhat laterally compressed, but not to sharp 

 edges. The maxilla (fig. 2, mx.) is very large, extending backwards beyond the 

 orbit, and overlapped above by a long and narrow supramaxilla (smx.), which 

 tapers to a point in front. The upper border of the maxilla is notched near its 

 anterior end just behind the prefrontal facette, and at the extremity of the 

 suborbital cheek-plate; its oral border is gently convex and curves slightly 

 inwards. The maxillary teeth resemble the teeth of the premaxilla, but, except 

 at the anterior end, they are somewhat larger, and they are often distinctly 



