HISTIONOTUS ANGULARIS. 93 



The majority of the fossil ganoids belong to the Palaeozoic and 

 Mesozoic age, and are only scantily represented now, the 

 sturgeon being one ; the ganoid-plates are united into a 

 shield over the head, but are detached over the body ; 

 the mouth is not furnished with teeth ; the tail is heterocercal. 

 The sub-order, Acipenseroidei, to which the Sturgeon belongs, is not 

 known with certainty to have come into existence before the 

 Eocene age, when it is represented by the Acipenser toliapicus 

 of the London clay. The living ganoids are, for the most part, 

 inhabitants of fresh waters; but many of the extinct forms are 

 associated with marine animals, therefore they probably inhabited 

 the sea. 



The Order Teleostei includes the great majority of the fish of the 

 present day. The skeleton is partially ossified, distinct cranial bones 

 and a lower jaw. The osseous column consists of completely ossified 

 vertebrae, hollow at both ends, ampJncoetous, the tail symmetrical. 

 The last vertebra has a central position in the base of the fin, and 

 united to a flat fan-like bone. In some, as the SafmomdcK, the last 

 vertebra is turned upwards. The scales are unusually thin, having 

 flexible plates overlapping each other ; some few are furnished with 

 ganoid scales, such as the file-fish, balistes, trunk-fish, ostracion, 

 and globe fish, Diodon. They seem to have appeared for the 

 first time in the cretaceous age, and to have attained their maximum 

 at the present day. 



I now proceed with a description of Histionotus angutaris, which 

 came into the possession of the County Museum last year, for 

 which we have reason to congratulate ourselves, as only three or 

 four specimens have hitherto been met with. It was first described 

 and figured by the late Sir Philip de M. Grey Egerton, Bart., 

 F.R.S., in the Memoirs of the Geological Survey, Decade viii., 

 1853. The uninterrupted dorsal fin, extending from near the 

 occiput to the tail, suggested the generic name of Histionotus, 

 and in this feature it resembles Opliiopsis. It has the characters 

 also of other genera, for instance, Photidophorus, in its scales, 

 Semionotus in the shape of its body, and Lepidotus in the shape of 



