LEPIDOTUS. 43 



of the dental crown is smooth ; but in one example of upper dentition from the 

 Isle of Wight (PI. XI, fig. 4) some of the teeth exhibit faint irregular wrinkles 

 radiating from the apex to an encircling wrinkle which forms a kind of cingulum 

 round the base (figs. 4 a, 4 h). 



In the hyoid arch (PL X, fig. 2), the epihyal [epJt.) is comparatively large and 

 stout, bearing about six branchiostegal rays, of which the uppermost {J>r.) forms a 

 long and narrow delicate lamina. The ceratohyal (ch.) is less than twice as 

 long as the epihyal, comparatively small in front of its constriction, and without 

 branchiostegal rays. The hypohyal (Iti/h.) is a short and stout bone, also constricted 

 in the middle. 



The branchial arches are unknown, but delicate calcified gill-supports are seen 

 in a specimen in the Beckles Collection (B. M. no. P. 6343). 



The preopercnlum, best seen in PI. IX, fig. 1, poj>.,is narrow and gently curved 

 at the angle. It is much overlapped by the postorbital cheek-plates, but extends 

 upwards to the hinder end of the squamosal in the cranial roof. Its ascending 

 limb is especially narrow, and marked with a slight rugosity or tuberculation only 

 near its upper end. Its lower limb is wider, with an irregular coarse rugosity 

 radiating downwards and backwards from the deep groove for the slime-canal. 

 The operculum and sul)operculura vary considerably, but some of the differences 

 observed are probably due to imperfections in preservation. As shown in PI. IX, 

 fig. 1, op., the operculum is somewhat wider below than aljove, and its maximum 

 width is about two-thirds of its depth. Its anterior margin is sigmoidally curved, 

 and its outer face is finely tuberculated, especially in the upper half. In the type 

 specimen of Lepidotus mantelli (PI. VIII, fig. 1, op.), the operculum appears to be 

 narrower, but this may be due at least in part to crushing and fracturing. In the 

 type specimen of L. fittoni (PI. VIII, fig. 2, op.), the bone is broken above and 

 behind, obscured in front with ironstone, and so much abraded that its outer 

 surface appears to be only rugose. In other abraded specimens its maximum 

 width scarcely equals two-thirds of its depth. The suboperculum (PI. VIII, fig. 2 ; 

 PL IX, fig. 1 ; sop.) is usually more than half as deep as wide, with a relatively 

 large anterior ascending process, and the outer face very feebly ornamented either 

 with rugai or tubercles. In the type specimen of L. utaiitelli, however, the sub- 

 operculum (PL VIII, fig. 1, sop.) is not half so deep as wide, and its outer face is 

 strongly tuberculated. The interoperculum (PL IX, fig. 1, lop.), is much extended 

 and tapering forwards, with the ornament as variable as that of the other bones. 

 Not more than six branchiostegal rays have been clearly seen, and the uppermost 

 is relatively large (PL X, fig. 2, hr.). There is no gular plate. 



The notochord must have been persistent, but at least in the anterior part of the 

 abdominal region there are surrounding ossifications. These are only imperfectly 

 known in a few Aveathered specimens, of which the best is shown in Text-fig. 18. 

 Encircling the upper part of the space left vacant by the decay of the notochord 



