420 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [May 14, 



Spatlwdactylus of Pictet, from the Neocomian formation of Switzer- 

 land. The position of the anal fin, as indicated by some scattered rays, 

 was immediately under the dorsal fin. There is every reason to suppose 

 that the structure of this fin was similar to that of the dorsal fin, 

 since the correspondence of the azygous fins in the Ganoid fishes 

 is of very general occurrence. 



Pal^ospinax pkisctjs, Egerton. 



This fish is described in the 7th article of the 13th Decade of the 

 Memoirs of the Geological Survey of the United Kingdom, from the 

 examination of several specimens in the collection of the Earl of 

 Enniskillen. In all these specimens, however, the position of the 

 second dorsal spine was not indicated. This desideratum is now 

 supplied by a recently acquired example of this fish from the same 

 locality, viz. Lyme Regis. The specimen exhibits the head and 

 trunk of the fish, with the exception of the hinder extremity, and 

 shows the two dorsal fin-spines in situ. It measures 16 inches 

 in length, and is probably 3 or 4 inches short of perfection. The 

 number of vertebrse preserved is 95. The first dorsal spine is 

 situated 2^ inches behind the occiput, and occupies a position over 

 the 16th vertebra. The second dorsal spine is fixed 7| inches from 

 the occiput and 5 inches behind the first, and is over the 50th 

 vertebra. A comparison of these measurements with the corre- 

 sponding parts in other recent and fossil spine-bearing Placoids 

 shows that Palceospinax made, in these respects, the nearest ap- 

 proach to the recent Cestracion, as is shown in the following 

 table : — 



Palceospiiiax 1st dorsal over the 16th vertebra, 2nd over the 50th. 

 Cestracion „ „ „ 15th „ „ „ 48th. 



Drepanephorus „ „ „ 24th „ „ „ 48th. 



Acanthias „ „ „ 24th „ „ „ 58th. 



The diminution in the size of the vertebra marking the commence- 

 ment of the caudal series, occurs at the 31st joint ; and immediately 

 below this joint there is a patch of light-coloured matter, which is 

 probably coprolitic. A little in advance of this a few delicate 

 fibres are preserved, which were probably derived from the ventral 

 fins. The frame-work of all the fins in this old form was more 

 solid than in the recent Placoids. In both dorsal fins and in the 

 pectoral fins the granular cutaneous outer investment was supported 

 by internal rays of a harder material than mere cartilage ; and con- 

 sequently these are preserved, although the softer parts have 

 perished. Those indicating the position of the ventral fins are 

 situated at five inches from the occiput, or about one third of the 

 entire length of the specimen. There is no trace of the anal fin, 

 although the outlines of the fish are tolerably well preserved — which 

 leads me to suppose that it was merged in the caudal fin, as it is 

 in the recent Acanthias. The spines of the dorsal fins are beauti- 

 fully preserved. The first is the smaller of the two, and is rather 

 stouter and more recurved than the nosterior one. The tubercular 



