ITS STRUCTURE, BULK, AND ASPECT. 75 



tlieir usual ichthyic position of displacement j the superior 

 frontal we find existing, as in the young of many animals, in 

 two pieces, C, C ; the nasal plate 1*, placed immediately in 

 advance of it, is flanked, as in the cod, by the anterior front- 

 als, D, D ; the posterior frontals, F, F, which, when viewed, 

 as in the print, from beneath, seem of considerable size, and 

 describe laterally and posteriorly about one-half the eye-orbits, 

 have their area on the exterior surface greatly reduced by 

 the overriding squamose sutures of the plates to which they 

 join ; and lastly, two of these overlying plates, E, E, — which, 

 occurring in the line of the lateral bar or beam, are of great 

 strength and thickness, and lie for two-thirds of their length 

 along the parietals, and for the remaining third along the su- 

 perior frontals, — represent the mastoid bones. Such, so far 

 as 1 have been yet able to read the cranial buckler of the 

 Asterolepis, seem to be the homologies of its component plates. 

 There were no parts of the animal more remarkable than 

 its jaws. The under jaws, — for the nether maxillary con- 

 sisted, in this fish, as in the placoid fishes, and in the quad- 

 rupeds generally, of two pieces joined in the middle, — were, 

 like those of the Holoptychius, boxes of bone, which enclosed 

 central masses of cartilage. The outer and under sides were 

 thickly covered with the characteristic star-like tubercles ; 

 and along the upper margin or lip there ran a thickly-set row 

 of small broadly-based teeth, planted as directly on the edge 

 Fig. 32. 



POETION OF UNDER JAW OF ASTEEOLEPIS (OUTER SIDE). 



(One-half nat. size). 



