304 



A. Smith Woodward — Eocene Siluroid Fishes. 



that the fossils indicate two distinct types, and it therefore seems 

 advisable to adopt the usual palasontological expedient of applying 

 a provisional name to each, merely for convenience of reference ; 

 and in the first case, at least, there can be little doubt that the 

 present determination will prove well founded. 



Arius Egertoni, Dixon sp. 

 1850. Silurus Egertoni, F. Dkon, Geol. and Foss. Sussex, p. 204, pi. xi. figs. 11-13. 



Pectoral Avcli and Spine. — The finest specimen figured by Dixon 

 among the types of this species is a right pectoral spine in natural 

 association with the clavicular element of the supporting arch (Brit. 

 Mus. No. 25612). A triangular dermal plate, ornamented with 

 irregularly- disposed, large conical tubercles, is firmly merged with 

 the clavicle in its middle portion, and extends backwards for a 

 distance equalling half the length of the spine; and the bone is 

 evidently preserved as far upwards as its sutural connection with 

 the supra-clavicle, though unfortuately mutilated near the rigid 

 lower symphysis. 



Of the spine itself, the National Collection comprises several 

 examples, which render it possible to define its characters completely. 

 These specimens vary considerably in size, though agreeing in every 

 other respect, and the beautiful fossil already mentioned is much the 

 largest, while one of the smaller ones (B. M. 25736) was originally 

 selected to show the form of the proximal articulation. All are of 

 the ordinary laterally-compressed shape, and, when well preserved, 

 exhibit an ornament of closely-approximated, short irregular ridges, 

 rising at intervals into small conical bosses. In the distal half of 

 the spine, the denticles upon the edges are large and recurved, but 

 more proximally they become much smaller, and the points incline 

 in the opposite direction. 



ff^T: 



J 



Figs. 1 and 2. Arius Egertoni, Dixon sp., M. Eocene, Brackleshani Bay, Sussex, etc. 

 Fig. 3. Arius ? Bartonensis, sp. nov., XJ. Eocene, Barton Clifi", Hampshire, etc. 

 a, median view of proximal articular end of Fig. 3. 



Dorsal Spine, etc. — The dorsal spine, associated by Dixon with 

 " Silurus Egertoni," corresponds so closely in the character of its 

 ornamentation with the pectoral appendage already referred to, that 

 there can be little doubt as to the correctness of the correlation. 



