48 WEALDEN AND PURBECK FOSSIL FISHES. 



Ti/f)i' Species. — Allirodon duuvillei (H. E. Sauvage, Bull. Soc. Geol. France [3], 

 vol. viii, 1880, p. 530, pi. xix, fig. 5) from the Lower Portlandian of Boulogne, 

 France. 



liemdrk^. — This genus is still known only by the dentition, which appears to be 

 less si)ecialised than that of any other Pycnodont. It ranges from the Kimme- 

 ridgian to the Senonian in Western Europe. 



L Athrodon intermedius, A. S. Woodward. Text-figure 19. 



1893. Athrodon intermedius, A. S. Woodward, Geol. Mag. [3], vol. x, p. 434, pi. xvi, fig. 1. 



Ti/2)e. — Left splenial dentition ; British Museum. 



Specific Characters. — Splenial bone comparatively elongated, 

 Avitli closely arranged teeth, mostly smooth and nearly round, a 

 few exhibiting an apical pit with feebly crimped margin, 

 disposed in about five or six irregular longitudinal series, the 

 largest forming a principal series near the symphysial margin of 

 the bone. 



Description of Specimen. — The only known example of this 

 intermedius, A. s. specics IS showu of the natural size in Text-fig. 19. Many of 

 spieniakientition, tliB tccth liave been mucli wom during life, but those of the 

 size — '^Purb'^ck largest scries seem to have been gently rounded, not pitted. 

 The^ t'^je^^^^ci- ^ome of the marginal teeth are broken away, but they appear 

 ™^^ (^- ^^- ^°- to have been all small. The slight apical pit is well seen in 

 the hindmost tooth of one of these series. 

 Horizon and Localiti/. — Purbeck Beds : Aylesbury, Buckinghamshire. 



Genus MESODON, Wagner. 



Mesodon, A. Wagner, Abliaudl. k. bay. Akad. Wiss., math.-phys. CI., vol. vi, 1851, p. 56. 



(?) Typodtis, F. A. Queiistedt, Der Jura, 1858, p. 781. 



Macromesodon, J. F. Blake, Mou. Fauna Cornbrasli (Pal. Soc, 1905), p. 32. 



Generic Characters. — Trunk discoidal, not produced at the caudal pedicle. 

 Head and opercular bones more or less ornamented with granulations ; cleft 

 of mouth very oblique ; teeth smooth, or wath feeble indentation and rugas ; 

 vomerine teeth in five longitudinal series, the lateral pairs often irregular ; splenial 

 bone with symphysial facette not deepened ; splenial dentition comprising one 

 principal series of teeth with three or more outer series and one or two inner 

 series, usually irregularly arranged. Neural and hsemal arches of axial skeleton 



