Actinopterygii Isospondyli. 



Ill 



appear to have been sometimes suddenly destroyed in shoals, 

 and buried at once by the fine calcareous mud. This circum- 

 stance is well illustrated in Wall-case No. 15, by several slabs 



FIG. 158. R/iinellus furcatus, Ag. (after Pictet and Humbert) ; Upper Cretaceous, Mount 



Lebanon. 



of fossil limestone from Hakel, near Beyrout, which are covered 

 with hundreds of their remains. 



The Salmonidse are scarcely known among fossils and very Table-case, 

 difficult to distinguish from the Clupeidse. It is usually possible 

 only to recognise the genera which still exist. Some surviving 



No. 49. 



FIG. 159. Capelin (Mallotus villosus), in nodule of Glacial Clay, Greenland. 



species are found fossilized in comparatively recent deposits, 

 and an interesting series of nodules is exhibited from the glacial 

 clays of Greenland, Norway, and the banks of the Ottawa River, 

 Canada, each enveloping a " Capelin" (Mallotus villosus). The 

 shape of the nodule (Fig. 159) in each case is observed to 

 correspond precisely with the contour of the enclosed fish, and 

 the concretion is probably due to the escape of gases from the 

 decomposing body leading to a concentration of mineral matter 

 at the spot from the clay around it. 



Near the Salmonidse are placed the remains of the Cretaceous Wal J~ < case 

 family of Saurodontidse, which have powerful teeth implanted 

 in distinct sockets on the margin of the jaw. Portheus attains No. 49. 

 a large size, as shown by the very fine slab of Portheus molossiis 

 from the Chalk of Kansas, U.S.A., exhibited in Wall-case 

 No. 16. More fragmentary specimens are shown from the 

 English Chalk. Closely allied are Ichthyodectes and Sauro- 

 cephalus. 



The large Cretaceous fish Pachyrhizodus (= Hypsodon in 

 part) is also perhaps related to the Salmonoids. It has power- 

 ful conical teeth firmly fixed to the jaws, and fragments from 

 the English Chalk have been erroneously referred to reptiles. 



Wall-case, 

 * 



