82 Messrs. Hancock & Atthey on Archichthys sulcidens. 



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 dimeiisions 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 esti- 

 mate may be made of the magnitude of the head. In Me- 

 galichthys the large jugular plates (and in that genus these 

 plates closely resemble those of Archichthys) are about the 

 length of the mandible, 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 Arch- 

 ichthys at 14 or 15 inches, the mandible cannot have been 

 less than 15 or 16 inches long. Now, as the head extends 

 considerably backwards beyond the articulation of the man- 

 dible, in some species for more than a third of the length of 

 the mandible, it would appear that the head of Archichthys 

 may be estimated as about 20 inches long, including, of course, 

 in this calculation the gill-plates. That this is not an over- 

 estimate is evident from the fact that the operculum and prge- 

 operculum together are between 4 and 5 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 9 

 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 Avhen we take into account the magnitude of the 

 oral weapons and the animal's superior activity, ^rc/acA^/iys 

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

 Carboniferous waters : it must have been quite able to hold 

 its own against Loxomma, or even against the more powerful 

 Anthracosau7-us. 



Notwithstanding the recent discovery of this large and 

 formidable fish, we are in possession of more information re- 

 specting it than has been attained in regard to many species 

 that have been acknowledged for years. The characters of 

 the dentition are perfectly determined : the mandible and prae- 

 maxilla have been obtained in a good state of preservation, with 

 the teeth attached. The gill- and jugular plates, too, have oc- 

 curred in most excellent condition, as well as several other 

 bones, including some that apparently belong to the thoracic 



