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Part III. — Twenty -fourth Annual Report 



examined in side view the ethmoid in esmarkii (E. } fig. 9, pi. xi.) is 

 seen to slope backwards quickly, whereas in minutus (fig. 6, ib.) and 

 luscus (fig. 3, ib.) it is more nearly vertical. 



There are few distinguishing features between the skulls of luscus and 

 minutus, even when they are compared side by side. To convert these 

 differences into characters by which the skull might be recognised apart 

 from the other is well nigh impossible, so closely are they related. 



A general contrast will, therefore, be made between the two. 



In two fish of the same size the skull of minutus was the larger — it 

 was slightly longer and higher. 



Seen from above, when the skull is resting on the vomer and the par- 

 asphenoid, the calcified base of the ethmoid (E.) is partly hidden by the 

 crest of the bone in luscus (fig. 4) ; in minutus the whole of the base is 

 visible (fig. 8). 



The processes from the parietals (P. pr.) are large, winglike, in luscus ; 

 they are narrow in minutus. The squamosals (Sq.) project posteriorly 

 farther in luscus than in minutus. The notch between the frontal (F.) 

 and post-frontal (pt.-F.) which receives the mucous canal passing 

 round the eye, is much smaller in minutus than in luscus. The frontal 

 in luscus contracts a little over the orbits and then expands again into a 

 broadened anterior extremity. In minutus it comes to its narrowest over 

 the orbits, and is continued forward with the same breadth. 



The breadth of the anterior end of the skull, measured from the outer 

 angle of one pre-frontal (pr.-F.) to the outer angle of the other, is in luscus 

 greater than in minutus. 



Side view. — The occipital spine (Oc. Sp.) of luscus (fig. 3) is much 

 higher than that of minutus (fig. 6). The part of the spine on the 

 frontal rises more rapidly in the former. 



The hind edge of the occipital spine may be straight, or it may be 

 slightly incurved just before reaching the occipital foramen. 



The front edge of the ethmoid lias less backward slope in luscus than 

 in minutus. 



In minutus the pre-frontal rises up to meet the outer corner of the 

 frontal : it raises the latter a little. In luscus it does not rise so much. 



Seen from below, the pre-frontal* is roughly of a quadrant shape in 

 luscus (fig. 12), and of a sextant shape in minutus (fig. 11). 



The parasphenoid (P.s) is more slender in minutus than in luscus. 



The brain-case is more spherical in shape in minutus than in luscus. 



Seen from behind, the squamosal (Sq.) bends outwards and upwards 

 in luscus (fig. 5). In minutus it projects more in a horizontal direction 

 (fig. 7). ' ' • I 



The opisthotic (op. 0.) forms in minutus a projecting angle where the 

 post- temporal articulates with it ; this angle was not noticed in luscus. 



The par occipital (par.-Oc.) of luscus is continued backwards in a pro- 

 jecting angle {Aug.), and in consequence the edge of the ex-occipital 

 (e.-Oc, fig. 3) curves downward in a concave sense to the articulation 

 with the shorter arm of the post-temporal. It is thus contrasted strongly 

 with the blunt termination of the par-occipital in minutus (fig. 6). 



The skull of esmarkii is long when compared with that of minutus. 

 An esmarkii measuring 15*5cm. in length had a skull equal in length to 

 that of a minutus 21cm. long. 



The ethmoid slopes back very quickly in esmarkii (fig. 9). The 

 frontal is narrow over the eyes, and the pre-frontals stand out prominently 

 laterally, but the breadth across them is small (fig. 10). 



The vomer projects further in front of the pre-frontals in esmarkii 

 fig. 13) than in minutus and luscus. 



