70 WEALDEN AND PURBECK FOSSIL FISHES. 



5. Ccelodus arcuatus, sp. nov. Plate XIII, fig. 5. 



Type. — -Vomerine dentition; Museum of Practical Geology, London. 



Specific Characters. — A species known only by the vomerine dentition, which 

 measures about 1*5 cm. in maximum width. Teeth of median series about three 

 times as broad as long, much constricted mesially, and much arched backwards; 

 apical pit well marked, crenulated round the margin, and the hinder face of the 

 tooth vertically plicated in its concavity. Teeth of two lateral series nearly equal 

 in size, and their width together not equalling that of the median series; apical pit 

 well marked, large, and crenulated round the margin. 



Description of Specimen. — The only known example of the vomerine dentition 

 (PI. XIII, fig. 5) is imperfect anteriorly but otherwise beautifully preserved. It 

 exhibits the usual transverse convexity, but the teeth of the paired series are on a 

 less steeply sloping surface than those in G. mantelli. The plication of the posterior 

 concavity of the median teeth is especially characteristic of the species. 



Horizon anil Locality. — Middle Purbeck Beds: Swanage, Dorset. 



Family Macr<>skmiiiu:. 

 Genus OPHIOPSIS, Agassiz. 



Ophiopsis, L. Agassiz, Neues Jahrb. f. Min., etc., 1834, p. 385 ; and Poiss. Foss., vol. ii, pt. i, 1844, 

 p. 289. 



Generic Characters. — Trunk much elongated, and the dorsal margin only 

 slightly arcuate ; head large or of moderate size. Marginal teeth acutely pointed. 

 Notochord surrounded by delicate ring- vertebras ; ribs ossified. Bifurcation of 

 dorsal fin-rays variable; fulcra present, comparatively stout at the base of the dorsal 

 and caudal fins. Paired fins relatively large ; dorsal fin ordinarily extending about 

 half the length of the back, high in front, low behind ; anal fin small and well 

 forwards ; caudal fin forked. Scales covering the whole of the trunk, in regular 

 series, united by peg-and-socket articulation, and often pectinated at the hinder 

 border; the scales of the middle of the flank scarce^ deeper than broad, few of 

 the ventral scales much broader than deep ; no enlarged ridge-scales. 



T//pe Species. — Ophiopsis procera (L. Agassiz, Poiss. Foss., vol. ii, pt. i, 1844, 

 p. 289, pi. xlviii, fig. 1) from the Lower Kimmeridgian (Lithographic Stone) of 

 Bavaria. 



Remarks. — The restoration of the type species of Ophiopsis given in Text- 

 fig. 25 is based chiefly on a specimen in the British Museum (no. P. 6939), in 



