PLEUROPHOLIS. 113 



of which those anteriorly are stouter than the rest and somewhat winged, can be 

 counted in front of the vein of calcite in the type fossil. The anal fin, which is 

 slightly less elevated than the dorsal, comprises 8 or 9 rays, which, when 

 adpressed, nearly reach the base of the caudal fin. Five fulcra are conspicuous 

 on the anterior margin. The caudal fin, known only in the type specimen, is 

 imperfect, and distorted upwards so that its precise shape is uncertain, but it seems 

 to have been forked. 



The only traces of scales on the trunk are immediately behind the pectoral 

 arch, but these may represent merely postclaviculars. Robust, smooth, over- 

 lapping ganoid ridge-scales, however, are conspicuous on both borders of the 

 caudal pedicle. The dorsal series begins above the middle of the anal fin, the 

 scales all very sharply pointed (PI. XXII, fig. 7b) and gradually increasing in 

 size until they pass into the upper caudal fulcra. The ventral series comprises 

 only three smaller and less acuminate scales, occupying the hinder half of the 

 space between the anal and caudal fins. 



Horizon and Locality. — Middle and Lower Purbeck Beds : Vale of Wardour, 

 Wiltshire. Purbeck Beds : near Weymouth, Dorset. 



Genus PLEUROPHOLIS, Egerton. 



Pleuropholis, P. M. Gr. Egerton, Figs, and Descripts. Brit. Organic Remains (Mem. Geol. Surv.), dec. ix, 



1858, no. 7. 



Generic Characters. — Trunk elongate-fusiform, with rounded back and sharp 

 ventral border; upper caudal lobe conspicuous. External bones smooth, or deli- 

 cately ornamented with rugoe and tuberculations ; sensory canal on cheek-plates 

 with branches ; mouth very small, with minute teeth ; maxilla more or less arched, 

 the oral margin convex. Vertebral centra annular; ribs short and delicate. 

 Fulcra present on all the fins. Pelvic fins well developed, but smaller than the 

 pectorals ; dorsal and anal fins longer than deep, opposite ; caudal fin forked. 

 Squamation complete ; scales thick and moderately overlapping ; those of the 

 middle of the flank excessively deepened, covering nearly the whole of it, each 

 strengthened within by a broad rib and exhibiting a peg-and-socket articulation ; 

 dorsal and ventral scales few, relatively small and rhomboidal. Lateral line 

 deflected, passing down the second or third deepened flank-scale and then 

 traversing the uppermost row of small ventral scales. 



Type Species. — Pleuropholis attenuata, from the English Middle Purbeck Beds. 



Remarks. — The osteology of the head in Pleuropholis is still very imperfectly 

 known, but its cheek-plates seem to resemble those of Pholidophorus in being only 

 in a single series. The most remarkable feature of the genus is the deflection of 

 the lateral line ; but it must be added that in one species from the Lithographic 

 Stone of Bavaria Miss Mary S. Johnston has also discovered slight traces of a 



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