122 FOSSIL FTSHES OF THE ENGLISH CHALK. 



radial ing, and partly reticulating rugas ; maxilla and dentary also rugose, but cheek- 

 plates smooth. 



Description of Specimens. — The type specimen (PI. XXIV, fig. 4) is supplemented 

 only by an imperfect skull (fig. 5), and perhaps by part of a dentary bone with 

 teeth (fig. 6). This species is therefore very imperfectly known. 



So far as preserved the skull closely resembles that of Osmeroides, but there 

 is ;i deeper median longitudinal depression in the frontal region. Remains of the 

 squamosal (fig. 5 <i, sq.) and postfrontal (ptf.) bones exhibit a coarse rugose orna- 

 ment, which is better shown in regularly radiating lines on the raised outer por- 

 tion of the frontal (//'.). The median frontal depression is comparatively smooth, 

 though there is some rugosity along the wavy line of the interfrontal suture. A 

 long and narrow supraorbital bone (spo.) occurs as in Osmeroides, but it is sharply 

 bent along its long axis, and only its upper lamina is marked by the coarsely rugose 

 ornament. The orbit is rather large, but the cheek-plates are also extensive. 

 There are three postorbitals (figs. 4, 5, po.), of which the lower is largest and 

 trapezoidal in shape, while the middle plate is comparatively small, long and 

 narrow. They are smooth, marked only by the ridge of the slime-canal along the 

 orbital margin, and with slight radiating wrinkles. The antorbital cheek- 

 plate (ao.) is elongate-triangular in shape, comparatively thick, and quite smooth 

 on the outer face. 



The mandibular suspensorium is nearly vertical, the articulation of the 

 mandible being directly beneath the occiput. The long maxilla (PI. XXIV, fig. 4, 

 rii,i'., and fig. 4 a) is truncated in front, has a straight oral border, and only deepens 

 backwards to form a facette which is overlapped by the supramaxilla (smx.). Its 

 flattened outer face is ornamented with coarse, reticulating rugse. The type 

 specimen shows in the anterior half of the bone the bases of attachment of a single 

 close series of rather large teeth on an inner ledge. The articulo-angular bone 

 (ag.) is apparently smooth in its upper portion, but is traversed by a longitudinal 

 groove below the articular facette, and here becomes coarsely rugose. The 

 dentary (d.) is also traversed by a deep longitudinal groove, which separates a 

 comparatively smooth upper portion from a coarsely rugose lower portion. In 

 the type specimen the oral border of this bone exhibits the bases of attachment 

 of a single close series of large teeth on an inner ledge, and of a close series of 

 small teeth on the extreme outer edge. In part of a left dentary (fig. 6), probably 

 of Dinelops, found isolated in the Lower Chalk of Kent, some of the teeth are 

 actually preserved. They are slender and styliform, quite smooth, with a very 

 small central cavity. One of the large inner teeth has a bluntly pointed apex, 

 while the small marginal teeth are capped by a sharp point of transparent enamel 

 (fig. 6 a). 



The width of the opercular apparatus is shown by the type specimen to be 

 about equal to that of the postorbital cheek-plates. The operculum (PI. XXIV, 



