ON AROHICHTHYS SULCIDENS. 395 



is certainly a largo species ; but the largest jugular plate we 

 have seen of that fish is scarcely more than seven inches long, 

 not half the length of those in question. And, moreover, its 

 form and enamelled surface are sufficient to distinguish it, 

 though in general character it has considerable resemblance to 

 the specimens under discussion. Except those that are altoge- 

 ther out of the question, the only other fishes of any considera- 

 ble size that occur in our coal-shales are the three large species 

 of Ctenodus : in this genus, however, the mandible is too short, 

 and the space in front between the rami too contracted to admit 

 of there being any large jugular plates. Unfortunately, these 

 two enormous plates are imperfect ; but what remains of each is 

 in an excellent state of preservation, and lies flattened out, the 

 form being completely retained : and there is no difficulty in 

 determining the entire contour ; for whilst one has only the pos- 

 terior extremity imperfect, this extremity in the other is entire. 



The right plate has the under surface exposed ; the anterior 

 portion of this is quite perfect, a small part only of the posterior 

 extremity, as just noticed, being wanting. In front it tapers 

 gradually to a point, and there is a notch on the inner margin, 

 about one inch and a quarter from the apex ; at this part the 

 surface is depressed diagonally, the depression being bounded 

 in front by a stoutish ridge. This plate, or, rather, as much of 

 it as remains, is twelve inches long and four inches and a half 

 wide. Only the posterior extremity of the left plate is present; 

 and this fragment is three inches and a half in length, and lies 

 with the upper surface exposed, with the inner margin in con- 

 tact with the outer margin of the other plate. The posterior 

 border is obtusely pointed ; but as the slope is shorter on the 

 outer than on the inner margin, the acumination is towards the 

 outer edge. 



By the aid of the two fragments, the form of the entire plate 

 is easily determined. It is elliptical or widely fusiform, with 

 the anterior extremity pretty regularly and gradually pointed, 

 the posterior end being more abruptly and excentrically acumi- 

 nated. When perfect, these huge jugular plates cannot have 

 been less than fourteen or fifteen inches in length, as, judging 



