134 Oeological Society. 



PROCEEDINGS OF LEAENED SOCIETIES. 

 GEOLOGICAL SOCIETY. 



March 9, 1887.— Prof. J. W. Judd, F.R.S., 

 President, in the Chair. 



The following communications were read: — 



1. " On Cliondrosteus acipetiseroides, Ag." By James W. Davia, 

 Esq., E.G.S. 



Sir P. Egerton described two species of Cliondrosteus from the 

 Lias of Lyme Regis, viz. C. acipenseroides, Ag., and C. crassior, Eg. 

 The author describes an unusually fine specimen from the same 

 locality, 44 inches long, the head, trunk, and tail being exception- 

 ally complete, whilst a considerable portion of the elements of the 

 vertebral column is preserved. 



The head is proportionately large and deeper than the body of the 

 fish. It has an almost circular outline with a diameter of about 

 9 inches, but the snout has been broken oflp during extraction. The 

 cranium was protected by dermal bones or scutes. The anterior 

 portion of the head, beneath the orbit, does not exhibit any traces of 

 external defence, thus diff'ering from existing Sturgeons. The fron- 

 tals, postfrontals, parietals, mastoid, and some of the occipital plates 

 are present : aU these bones are united by sutures. The external 

 surface of the dermal plates is coarsely striated or ridged ; the ridges 

 radiate for the most part from the centre towards the margin, the 

 surface being covered by strips of ganoine. The orbit is oval. The 

 base of the skull is formed by bones more completely ossified than 

 in the existing Sttirgeons : these are more extensive than in the 

 Teleostean fishes, being the equivalents of the sphenoid bones of the 

 latter. 



Sir P. Egerton, in his description of the genus Chondrostens, 

 states that the elements of the scapular arch, which in recent 

 Sturgeons are three in number, are reduced to two in the fossil 

 genus by the coalescence of the scapula and the coracoid. The 

 Author describes it as composed of a series of three bones, supra- 

 ecapula, scapula, and coracoid (or clavicula). The last is united 

 with the pectoral fin by two bones, apparently representing the 

 radius and ulna of Owen (coracoid and scapula of Parker). The 

 pectoral fin is large and comprised fortj^-two rays. The mandibles 

 and maxillaries are large and well ossified, in this respect difi'ering 

 from existing species ; there is no evidence of teeth. From the 

 position of the respective maxillary and premaxillary bones in this 

 specimen there can be no further doubt that the small bifurcated 

 bone of G. acipenseroides, Ag., described as the maxillary bone, is 

 really the premaxillary. 



Bony neurapophyses are preserved in the anterior portion of the 

 body. There is no trace of the vertebral column nor of ribs or 

 hsemapophyses, except in the caudal fin, where haemapophyses sup- 



