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On Fossil Fishes, particularly those of tJw London Clay. By 



Professor Agassiz. With a Plate. 



(Concluded from p. 327 of vol. xxxix. of this Journal.) 



To give an idea of the accuracy to which it is possible to attain in 

 making a comparative study of the Sheppey Fish, I will give in this 

 place a description of one of the most common species in this formation, 

 the Scicenurus Bowerbankii. I add to this description an outline 

 restoration of the entire animal. (Plate VI.*) This fish has the body 

 short, high, and much compressed, resembling in this respect tho 

 Sargi, or even the Doreys (Zeus). Its height, taken at the front 

 margin of tho anal fin, is contained twice and a half in its length ; 

 its thickness, even taking into consideration the pressure com- 

 mon to the Sheppey fossils, is comprised four times in its height ; 

 its head participates in the same characters as the trunk; it is 

 high, compressed, and anteriorly truncated. It is as long as high, 

 and its length is to the total length of the body as two to seven. 

 The front forms a straight line, descending obliquely from a pro- 

 minence above the eyes ; the nape is nearly horizontal, rising gra- 

 dually towards the dorsal fin. The snout is almost vertically trun- 

 cated, and forms a sharp-edged keel. 



The eye is very large, and occupies more than a third of the total 

 height of the head ; it is placed very high, nearly on a level with 

 the forehead, in the centre between the end of the snout and the 

 posterior margin of the preoperculum. The sclerotic capsule which 

 surrounds it is strong, and well preserved in the majority of the 

 specimens. 



The construction of the. cranium presents several striking pecu- 

 liarities ; its upper surface exhibits a line broken into three nearly 

 equal portions ; the hinder portion, or the nape, is oblong, gradually 

 contracted from behind anteriorly, and divided into two portions by 

 the central crest of the cranium, which appears to have been very 

 thin and very high. This central crest extends hindward, as far 

 as the first dorsal ray. The two parietal crests which circumscribe 

 this upper oblong portion of the nape are very prominent, but some- 

 what slender ; they extend for a long way hindwards, where they 

 form the articulation of the suprascapulary ; they likewise extend 

 into the projecting angle above the eyes. The same is the case with 

 the central crest ; the two parietal grooves extended, therefore, to 

 above the eyes, becoming gradually smaller, and rising to tlie level 

 of tho front. The surface of the na^e consequently formed a sort 

 of elongated roof raised on the median line, and bounded on the 

 two sides by tho parietal crests. The superior occipital bone ad- 

 vances, en biseait, as far as the central crest, between the two fron- 

 tals, which extend hindward half the length of the nape. Three 



* The Plate in our next Number. 



