so-called Microdon nuchalis^ Dixon. 343 



The specimen is shown of the natural size in Mr. Dixon's 

 figure already quoted, though the details unfortunately are 

 but slightly marked. It comprises a large portion of the 

 crushed head, the pectoral and pelvic arches, the abdominal 

 portion of the vertebral column, with some remains of dorsal 

 interspinous bones, and a fragment of the caudal region. 

 None of the sutures between the bones of the head can be 

 distinguished, but part of the supraoccipital is conspicuous, 

 from its being extended upwards in the form of a strong, 

 laterally compressed, triangular crest. The facial profile is 

 very steep and the orbit is relatively large. The remains of 

 two or three branchiostegal rays are recognizable^ and possibly 

 also the bases of some minute hollow teeth in the jaws. The 

 vertebrae, with their arches, are well ossified, and there are 

 apparently ten in the abdominal region, while all but six of 

 the caudal have been destroyed. The centra are much 

 broken, so that it seems impossible to determine their exact 

 form and characters. As in the skull, the elements of the 

 pectoral arch are undistinguishable, and these are somewhat 

 displaced backwards, both the so-called " pelvic " bones and 

 the first interhsemal of the anal fin being crushed together 

 with them. Of the pectoral fins no fragments remain ; but 

 each of the pelvic fins is represented by a single robust spine, 

 all the soft rays, if ever present, having disappeared. The 

 three small spines in advance of the anal fin are also pre- 

 served ; and above the vertebral column, behind the supra- 

 occipital crest, are a number of large, broad, interspinous 

 bones, evidently testifying to the original presence of a very 

 high dorsal fin. There are no traces of scales, which must 

 thus have been either very delicate or absent. 



Such being the only characters shown by the fossil, it is 

 obviously impossible to determine its exact position in the 

 Teleostean series by a reference to ordinary systematic diag- 

 noses. A careful comparison, however, with known types 

 can leave no doubt that the Chalk species is an ally of the 

 existing Carangidse, and must thus be placed in this family 

 or among the less differentiated forms, ancestral to the Caran- 

 gidge, which flourished in the later Mesozoic seas. So far as 

 preserved, indeed, the fossil is almost identical with certain 

 more perfect specimens from the Upper Chalk of Mount 

 Lebanon, which have been referred, with much probability of 

 correctness, to the still- surviving genus Platax *. The only 



* F. J. Pictet, ' PoissoDS Fossiles du Mont Liban,' 1850, p, 19, pi, ii. 

 fig. 1 ; F. J. Pictet and A. Humbert, ' Nouv. Rech. Poiss. Foss. M. Liban,' 

 1866, p. 48, pi. iv. figs. 1-3 ; J. W. Davis, " On the Fossil Fishes of the 

 Chalk of Mount Lebanon," Trans. Roy. Dublin Soc. [2] vol. iii. (1887), 

 p. 624, pi. XXV. tig. 4. 



