PLEUROPHOLIS. 115 



smooth. Pelvic fins arising midway between the pectorals and the anal ; dorsal 

 fin, with 10 rays, arising opposite the origin of the anal fin, which comprises at 

 least 12 rays, and arises nearly midway between the pectoral and caudal fins. 

 Scales smooth, not serrated. 



Remarks. — This species is still known only by the type specimen discovered by 

 Mr. H. W. Bristow, which is now missing. The above definition is based on 

 Egerton's description and figure (reproduced here in Text-fig. 35a). 



Horizon and Locality. — Middle Purbeck Beds : Apsel Lane, Sutton Mandeville, 

 Wiltshire. 



2. Pleuropholis formosa, sp. nov. Plate XXII, fig. 8; Plate XXIII, figs. 8—11; 



Text-figure 36. 



Type. — Nearly complete fish ; British Museum. 



Specific Characters. — A slender, regularly fusiform species, attaining a length 

 of about 7 cm. Length of head with opercular apparatus about equalling maximum 

 depth of trunk, and contained from five to six times in total length of fish ; caudal 

 pedicle about two-thirds as deep as deepest flank-scale. Opercular bones smooth. 

 Pelvic fins arising slightly nearer to the anal than to the pectorals ; dorsal fin, 

 with 9 or 10 rays, arising just behind the origin of the anal, which is somewhat 

 larger, with 11 or 12 rays, of which the length of the foremost is somewhat less 

 than the depth of the trunk at its insertion. Scales smooth, not serrated. 



Description of Specimens.— The type specimen, though fractured, seems to 

 exhibit the general shape of the fish, with the complete caudal fin and enough 

 remains of the other fins to indicate their position and proportions (PI. XXIII, 

 fig. 8). Parts of five smaller specimens on the same slab of limestone show various 

 additional details ; and several distorted examples obtained by the Rev. W. R. 

 Andrews and others from the same horizon and locality confirm and extend our 

 knowledge of the osteology of the species. 



All the external bones of the head and opercular apparatus seem to have been 

 smooth, covered with shining ganoine, and marked only by the occasional ridges 

 and pores of the slime-canals. The cranial roof slopes gently downwards and 

 forwards, without any marked bend in the frontal region; but in the basicranial 

 axis the parasphenoid, as seen in side view crossing the orbit (PI. XXIII, fig. 9, pas.), 

 is much arched, inclining downwards and forwards as it leaves the pro-otic region, 

 and then turning upwards to the short ethmoid region. The orbit is very large, 

 and there is a delicate ossification in the sclerotic. The single series of cheek- 

 plates round the orbit is narrow, and marked only by the large slime-canal, which 

 traverses the orbital margin as usual. The mandibular suspensorium is much 

 curved forwards, so that the quadrate articulation is beneath the anterior half of 

 the orbit, and the gape of the mouth is very small. The entopterygoid (PL XXIII, 



