HISTIONOTUS ANGULARIS. 95 



The depth of the shoulder-girdle is 25 mm., and the breadth 

 of the post-clavicular plates 5 mm. The opercular apparatus is 

 well preserved, showing distinctly the operculum (op.), sub- 

 operculum (s. op.), inter-operculum (i. op.), and pre-operculum 

 (p. op.), besides a few branchiostegal rays. These, like the post- 

 clavicular plates of the shoulder-girdle, are all enamelled. 



The bones of the head are much crushed. The maxillse, although 

 perfect, are displaced ; and a portion of the right premaxilla is 

 preserved, showing seven teeth with part of the eighth. These 

 teeth are styliform, slender, straight, and smooth, and appear to 

 decrease in size from front to back. The largest is 2 mm. in 

 length. The vomerine bones are hidden, which unfortunately 

 prevents our ascertaining whether or not the roof of the mouth 

 is armed with teeth. The orbit is obliterated by the intrusion 

 of the underlying skull-bones. 



The scales of the body are small as compared with those of 

 Lepidotus, and are not so lustrous. Those of the flank measure 

 6 mm. in depth and 2 mm. in breadth. They are rhomboidal in shape, 

 finely pectinated on the posterior exposed margin, arranged obliquely 

 in rows from the dorsal to the ventral region, twelve in a series. 

 The lateral line from head to tail extends along the middle of the 

 flank. Between the last ray of the dorsal fin and the base of the 

 caudal are three double-cone-shaped lustrous ridge-scales, which 

 may have served to strengthen this attenuated part of the body, 

 enabling it to resist the strain upon it when the caudal fin was in 

 action. 



Length of body ... ... ... ... 1'80 m. 



,, tail, upper lobe ... ... ... 0'50 m. 



lower lobe 0'30 m. 



head 0'46 m. 



Breadth of head (HO m. 



EXPLANATION OF PLATE. 



Histionotus angularis, Egerton ; right lateral aspect of fish, 

 nat, size. Middle Purbeck Beds, Swanage, Dorsetshire. br. 



