48 FOSSIL FISHES OF THE ENGLISH CHALK. 



fig. 13, III. Immediately within this series there is another close row of somewhat 

 larger teeth, partly shown in both of the figures cited (ii). Further inwards there 

 occurs a widely spaced series of six large teeth (i), of which the foremost at the 

 symphysis is broken away in both of the specimens figured. These large teeth are 

 smoother than those of the palato-pterygoid arcade, and only compressed to a sharp 

 edge quite at the apex, where the barb is scarcely if at all observable. Their mode 

 of replacement is the same as that already described, and the fourth tooth in the 

 original of fig. 13 is accompanied by its successor. The third tooth from the 

 symphysis is usually the largest member of the series. The general aspect of 

 the jaws is diagrammatically represented in Text-fig. 10, p. 45. The ceratohyal 

 (PL XII, fig. 2 a) is much elongated and laterally compressed. 



The opercular apparatus (PI. XII, fig. 1 o) is scarcely known. The preoper- 

 culum (poj).) is deep and narrow, almost without a lower limb, but slightly 

 pectinated at the lower border. The operculum (oj).) is thin and ornamented, at 

 least in its anterior portion, with sparse rows of small tubercles. 



The post-temporal (PI. XII, fig. 1, ptt.) is an elongate-triangular lamina of 

 bone, with its anterior apex impinging on the supraoccipital. On its outer face 

 some short, fine, tuberculated ridges radiate from its truncated postero-external 

 angle. 



Trunk named Plintho2)horus rohustns. — The trunk of Cimolichthijs lorcsiensis has 

 not hitherto been found in association with the head ; l)ut the specimen shown of 

 one half the natural size in PI. XII, fig. 5, is probably referable to this species. It 

 has already been described by Dr. Giinther, loc. cit., 1864, under the name of 

 Plinthojjlioriis rohustns. The fossil is a little distorted in front and below, but the 

 trunk is shown to have been elongate-fusiform, with the abdominal region longer 

 than the caudal region. A few of the anterior vertebrse are lacking, but the total 

 number in the column must have been originally about 60. The vertebral centra 

 are slightly longer than deep, each much constricted in the middle and strengthened 

 by a few longitudinal ridges. The ribs are slender and not much arched, evidently 

 not reaching the ventral border. The neural spines in the abdominal region 

 are also slender ; but those in the caudal region, like the opposite haemals, seem to 

 be somewhat stouter, rather short and curved backwards, until they reach the 

 caudal fin, where they are quite recumbent and thickened. The pectoral fins {pet.) 

 are long and narrow, comprising 12 rays, of which the unjointed bases are 

 preserved. The pelvic fins {plv.), which are still more imperfect in the fossil, seem 

 to have been nearly as large as the pectorals, with 10 or 11 rays. They have a 

 broad base supported by a pair of much-expanded, laminar pelvic bones. The 

 dorsal fin {do.) is completely within the anterior half of the trunk, terminating be- 

 hind opposite the insertion of the pelvic pair. It comprises at least 14, perhaps 16 

 rays, of which the foremost are much the longest and stoutest. The anal fin is 

 remote, and must have been much smaller than the dorsal, but it is only represented 



