PRANEROPLEUROX ANDE.P.SONI. 



49 



expanded at the ends, are adapted to them. These interspinous 

 bones increase in length from before backwards to beyond the 

 middle of the dorsal fin, and support the fin-rays, whose bases are 

 broad and solid, while they divide into a series of branchlets at their 

 ends. There may be more than one tin-ray to each interspinous bone. 



The dorsal fin, commencing with tlie posterior half of the body, 

 gradually increases in height posteriorly, as its upper margin remains 

 parallel with the axis of the body, while the dorsal line of the body 

 converges towards that axis ; the fin terminates posteriorly in an 

 almost vertically trmicated extremity. 



The ribs attain a considerable lengtli, even close to the head, and 

 are continued through the whole length of the abdomen, passing 

 gradually into the subcaudal bones. They are well ossified, and 

 hence, in the fossil state, they stare through the thin integumentary 

 scales of the fish so as to suggest its generic name. 



The anal fin is somewhat lanceolate in shape, inclined downwards 

 and backwards, and so long that its lower extremity is as distant 

 from the axis of the body as the upper edge of the dorsal. It is 

 supported by interspinous bones like those of the dorsal fin. 



The inferior lobe of the caudal fin commences immediately behind 

 the anal, and its rays appear to be supported by similar interspinous 

 bones, at least anteriorly. It can be traced backwards to near the 

 extreme end of the body. The superior lobe, on the other hand, 

 seems to have been obsolete. 



Explanation of Plate III. 



Fig. 1. Plianeropleiii on Andersoni, two-thirds of the natural size. From a specimen 

 in the British Museum, No. 26120. 



Fig. 2. Head of a specimen in the Museum of Practical Geology. The upper contour 

 of the cranium seems to be slightly distorted. Natural size. 



Fig. 3. Caudal extremity of a specimen in the British Museum, exhibiting the anal 

 fin, A scale of Hohptychius lies above the end of the tail. 



Fig. 4. Hinder part of the body, with ribs, neural arches, interspinous bones, and im- 

 pression of the caudal part of the tapering notochord. In the Museum of 

 Practical Geology. 



Fig. .5. Head and body, with the opercular apparatus and impressions of the ribs and 



neural arches nearly undisturbed. In the Museum of Practical Geology. 

 Fig. 6. Teeth magnified. 

 Fig. 7. A scale magnified. 



T. H. Huxley. 



Jermyn Street, Nov. 1, 1861. 



10 D 2 



