50 WEALDEN AND PURBECK FOSSIL FISHES. 



Mus. Roy. Hist. Nat. Belg., vol. v, 1911, fig. 11, p. 30) the limits of the vomer and 

 mesetlimoid arc erroneously indicated, the posterior digitate process of the parietal 

 is omitted, and the scales at the origin of the pelvic fins are incorrectly shown. 

 Crushed and broken specimens cannot be readily interpreted. 



The geological range of typical species seems to be from the Kimmeridgian to 

 the Wealden inclusive. 



1. Mesodon daviesi, A. S. Woodward. Plate XII, figs. 1, 2. 



1890. Mesodon' daviesi, A. S. Woodward, Proc. Zool. Soc, p. 351, pi. xxviii, fig. 5. 

 1895 Mesodon daviesi, A. S. Woodward, Catal. Foss. Fishes B. M., pt. iii, p. 201. 



Type.- — Nearly complete fish ; British Museum. 



Specific Characters. — A species attaining a length of 25 cm. Maximum depth 

 of trunk somewhat less than the length of the fish without caudal fin ; head with 

 opercular apparatus contained about three-and-a-half times in the same length ; 

 back gently rounded, and dorsal fin arising at the highest point. Principal splenial 

 teeth rounded and smooth, about twice as broad as long, flanked externally by two 

 series of smaller teeth, which are also smooth and often broader than long. Dorsal 

 and anal fins about equally elevated, the latter with 29 or 30 supports and four-fifths 

 as long as the former, which has 38 or 39 supports. Dorsal and ventral ridge-scales 

 each with a row of four or five small denticles which increase slightly in size 

 backwards. 



Description of Specimens. — The type specimen (PI. XII, fig. 1), with its 

 incomplete counterpart, exhibits all the principal characters of the species, except 

 those of the paired fins and the serration of the ridge-scales. A second smaller 

 specimen, apparently of the same species, in the British Museum (no. P. 4381), has 

 a slightly larger head, and agrees well with a more imperfect small specimen in 

 the Dorset County Museum. 



The head-bones as preserved in the fossils exhibit a fibrous texture, and the 

 only external ornament is a radiating reticulation, without any tubercles. The 

 parietal in the type specimen bears the usual large posteriorly-directed process with 

 digitate extremity, and the supraoccipital ends "abruptly, without any upward 

 production. The orbit is as small as in the type species, and all the characteristic 

 Pycnodont features are vaguely seen in the facial region. The small cleft of the 

 mouth is, as usual, inclined slightly upwards and backwards. The vomerine 

 dentition is seen only in edge-view, but in B. M. no. V. L381 it is shown to have 

 been slightly convex from side to side. The splenial dentition, partly exposed 

 from the attached face in the same specimen, exhibits the principal teeth Hanked 

 outside by two series of teeth, which are also broader than long, while the inner 

 slightly exceed the outer in size. As shown in the type specimen (PI. XII, tig. 1 a), 



