396 MESSRS. HANCOCK AND ATTHEY 



from the specimens, it would seem evident that the fragment 

 (which is twelve inches long) of the right plate has lost two or 

 three inches of its posterior extremity. 



A fragment of a bone lies on the outer margin of the right 

 plate, which in all probability is the anterior central plate ; but 

 it is too imperfect to admit of any decided opinion. 



The bones originally supposed to be jugular plates were folded 

 and much crumpled and distorted, so that their form and di- 

 mensions could not be determined with certainty. We are now 

 disposed to consider these to be certain cranial bones, of the 

 exact nature of which we have not yet satisfied ourselves. 



From the size of the jugular plates a very fair estimate may 

 be made of the magnitude of the head. In Megalichthys the 

 large jugular plates (and in that genus these plates closely re- 

 semble those of Archichthys) are about the length of the mandi- 

 ble, or rather a little shorter, allowing for the projection of the 

 rami in front. If therefore we take this as a guide, and are 

 correct in estimating the jugulars in Archichthys at fourteen or 

 fifteen inches, the mandible cannot have been less than fifteen 

 or sixteen inches long. Now, as the head extends considerably 

 backwards beyond the articulation of the mandible, in some 

 species far more than a third of the length of the mandible, it 

 would appear that the head of Archichthys may be estimated as 

 about twenty inches long, including, of course, in this calcula- 

 tion the gill-plates. That this is not an over-estimate is evident 

 from the fact that the operculum and prseoperculum together are 

 between four and five inches wide. The width of the head can 

 also be very correctly estimated : it could not be less than ten 

 or twelve inches. This is evident when we recollect that the 

 joint width of the jugulars is nine inches, that the mandibular 

 rami are each an inch thick, and that it is not improbable that 

 there were small external jugular plates lying between the rami 

 and the outer margins of the large jugulars. 



These are formidable proportions, indicating a very powerful 

 creature ; and when we take into account the magnitude of the 

 oral weapons and the animal's superior activity, Archichthys 

 must have been no mean rival to the large Amphibians of the 



