144 WEALDEN AND PURBECK FOSSIL FISHES. 



partial fusion of the haemal spines at the base of the caudal fin, and an increased 

 development of the intermuscular bones, some of them may have become Clupeidae. 

 By nearly the same changes, such genera as Pachythrissops and Thrissops may 

 also have passed into the Ghirocentrus-hke fishes, which were as numerous in the 

 Cretaceous fauna as the Elopines and Olupeoids, and are represented at the present 

 day by a genus (Chirocentrus) which retains a remnant of the primitive spiral 

 valve in the intestine. 1 



It is therefore interesting to compare the fishes of the Wealden and Purbeck 

 estuary with those of the contemporaneous seas in the European area. It is only 

 unfortunate that the latter are thus far very imperfectly known. Fish-remains are 

 not uncommon in some of the marine Neocomian formations of France which seem 

 to be contemporary with at least the later Wealden deposits, but they are all very 

 fragmentary. 2 So far as determinable, nearly all of them are typically Jurassic ; 

 though it should be remembered that these are durable fossils such as the teeth 

 and fin-spines of sharks, and the teeth and jaws of Pycnodonts and Lepidotus. 

 More delicate skeletons may have been destroyed beyond recognition, as suggested 

 by the discovery of an otolith which may be Clupeoid. 3 Among these fossils, 

 however, both in France and in Switzerland there are a few Selachian teeth 4 so 

 closeby similar to those of the Lamnidge that they evidently indicate the appearance 

 of the modern type of shark which became so abundant and widely spread in the 

 later Cretaceous seas. Well-preserved fishes in another Neocomian formation in 

 the Voirons, Switzerland, 5 include recognisable forerunners of the Chirocentrids 

 (Spathodactylus neocomiensis) and Clupeoids (Crossognathus sabaudianus, Glupea 

 <titfni tin, and Glupea voironensis) , those referred to Glupea itself showing distinctly 

 the characteristic ventral ridge-scutes. The Clupeoid Grossognathus also occurs in 

 the Hilsthon of Hanover, which seems to correspond with the uppermost part of 

 the Weald Clay. The marine fish-fauna of Europe before the end of Wealden 

 times was thus distinctly in advance of the estuarine fauna so far as known, and 

 approached the later Cretaceous fauna in its Lamnid sharks, Chirocentrids, and 

 Clupeoids. 



The nearly contemporaneous estuarine deposit on the coast of Bahia, Brazil, to 

 which reference has already been made, shows that the Lower Cretaceous fish- 



1 Cuvier and Valenciennes, Histoire Naturelle ties Poissons, vol. xix (1846), p. 100, pi. 565. 



2 M. Leriche, " Sur quelques Poissons du Cretace du Bassin de Paris," Bull. Soc. Geol. France, 

 [4] vol. x (1910), pp. 455—469, pi. vi. 



* Otolithus (Clupeidarum ?) neocomiensis, F. Priem, "Poissons Fossiles du Bassin Parisien" 

 (Publ. Ann. Paleont,, 1908), p. 37, text-figs. 11—14. 



4 Lamna (Odontaspis) gracilis, L. Agassiz, Poiss. Foss., vol. iii (1843), p. 295, pi. xxxviin, 

 figs. 2—4. Odontaspis macrorhiza mut. infracretacea, M. Leriche, Bull. Soc. Gcol. France, [4] vol. x 

 (1910), p. 459. 



F. J. Pictet, " Description des Fossiles du Terrain Ne'ocomien des Voirons" (Mater. Paleont. 

 Suisse, ser. 2, 1858), pp. 1—54, pis. i— vii. 



