158 A. S. Woodicard — A New Pycnodont ffish. 



III. — On a New Species of Pycnodont Fish (Mesodon Bamoni) 

 from the Portland Oolite. 



By A. Smith "Woodward, F.G.S., F.Z.S. 



THE Fossil Fishes of the English Portlandian Formation are as 

 yet almost unknown, and every small contribution to the sub- 

 ject is thus of interest. Ischyodus Townsendi, ] Microdon pagoda, 2 the 

 pai'tially described Caturus angustus, 3 an undetermined species of 

 Thrissops,* and an undescribed species of Mesodon, 5 appear to be the 

 only forms hitherto recorded ; and to these may be added a large 

 bony fish allied to Ditaxiodus, represented by jaws in the British 

 Museum. 



The species of TJirissops and the, isolated jaws just mentioned 

 require longer study and more detailed comparison than the present 

 writer has yet been able to undertake for their satisfactory determi- 

 nation ; but the dentition of Mesodon seems to be so common and 

 typical a fossil of the Portland Beds, exhibiting such well-marked 

 characters, that it will be convenient at once to apply to the fish it 

 represents a defined specific name. Mandibular rami with teeth of 

 the form here referred to have been recorded in error under the 

 name of " Pycnodus Buclclandi, Ag." ; and a figure of one fine 

 specimen, now in the British Museum, is given in the Supple- 

 ment to Mr. Robert Damon's "Geology of Weymouth," pi. viii. 

 fig. 9. This fossil is a left splenial bone, showing nearly all the 

 teeth in position, and its principal characters are repeated in five 

 other specimens in the same collection. 



The bone in question is comparatively short and broad ; and the 

 teeth of the principal series are transversely elongated, not less than 

 twice as broad as long. These teeth are regularly arranged, with 

 narrow interspaces, and the outer extremity of each is somewhat 

 broader and more truncated than the inner extremity, which exhibits 

 a slight tendency towards tapering. The inner series of rounded teeth 

 is relatively larger than usual in the genus, and is irregularly spaced ; 

 while still nearer the inner border are five smaller round teeth, with 

 no definite regular arrangement. The outer teeth are smaller than 

 those of the principal inner row, and seem to be disposed in three 

 close but indefinite series, with a trace of a fourth marginal series ; 

 they vary in size and form indiscriminately, some being imperfectly 

 hemispherical and others transversely elongated ; and none exhibit 

 a direct linear arrangement, although the median of the three series 

 is marked by its teeth being of slightly less size than those of the 

 other two. In another specimen the fourth or outer marginal series 



1 Sir Philip Egerton, Proc. Geol. Soc, vol. iv. (1843), p. 156. E. T. Newton, 

 Chimseroid Fishes, Brit. Cret. Rocks (Mem. Geol. Survey, 1878), p. 33, pi. xi. 



2 Smith Woodward, Geol. Mag. [3] Vol. VI. (1889), p. 454. Pycnodus pagoda, 

 J. F. Blake, Quart. Journ. Geol. Soc, vol. xxxvi. (1880), p. 228, pi. x. fig. 10. 



3 L.Agassiz, Poiss. Foss., vol. ii. pt. ii. (1843), p. 115. 



* Smith Woodward, Geol. Mag. [3] Vol. VI. (1889), p. 455. 



6 Woodward and Sherborn, Cat. Brit. Foss. Vertebrata (1890), p. 121. Pycnodus 

 Bucklandi, J. F. Blake (non Agassiz), Quart. Journ. Geol. Soc, vol. xxxvi. (1880), 

 p. 227, and E. Damon, Geol. Weymouth (1860-88), Suppl, pi. viii. fig. 9. 



