﻿Sir Philip Grey-Egerton — On smne New Pycnodonts. 53 



sketches of three Pycnodont mandibles which I considered could 

 not all be referred to Pycnodus toliapicus. For thirty years the 

 subject escaped my memory, until the examination of the Folkestone 

 specimen described in a previous article reminded me of the 

 occurrence, and induced me to make a comparison between it and 

 the Bowerbankian specimens now in the British Museum. Two of 

 these belong no doubt to Pycnodus toliapicus. They are right and 

 left mandibles, and so nearly of a size that they might have belonged 

 to the same individual. The right jaw has three rows of teeth. 

 Those of the inner row are the largest. They are five in number 

 and elliptic in form, agreeing in the latter respect with the descrip- 

 tion given by Agassiz : "The principal teeth are elongated and 

 rounded at the extremities." The second row contains six teeth 

 very much smaller than those of the inner row, and of ovoid out- 

 line ; the third row has four teeth of similar figure to the preceding 

 ones, but rather smaller. The left mandible corresponds in these 

 details with the right, but has in addition an inner row of small 

 teeth between the principal row and the symphysis, of which three 

 anterior ones are apparently in situ. The occurrence of this inner 

 row of denticles is not in my opinion of specific signification when 

 the other characters correspond so closely. It is constant in Gyrodus, 

 but in Pycnodus, as I have before stated, it is by no means a charac- 

 teristic feature. When it is present the component teeth are invariably 

 smaller than any others. On comparing these specimens and the 

 figure of Pycnodus toliapicus given on pi. 72 a. fig. 55, of vol. ii. 

 pt. 2, of the Poissons Fossiles, with the figure of Periodus Koenigi, 

 figs. 61-2 on the same plate, and the specimens in the British Museum 

 and my own cabinet, I am at a loss to discover any difference either 

 generic or specific between them. The specimens of Periodus have 

 been more rubbed down by use, and the discrepancy in the form of 

 the crowns is due to the unequal attrition of the vomerine teeth. 



The third specimen from Dr. Bowerbank's collection is a right 

 mandible in beautiful preservation. It is quite as large as Ccelodus 

 ellipticus described above, and contains three rows of teeth. The 

 inner or principal row (PL III. Fig. 2 a) has five normal teeth in 

 series and a sixth, the anterior one, replaced by what I have 

 designated a twin tooth (PL III. Fig. 2t). The regular teeth of 

 this row are larger and more obtusely oval than those of Pycnodus 

 toliapicus. The twin tooth is divided into a circular denticle, rather 

 irregular, and a crescentic portion embracing the inner periphery of 

 the former. I have already alluded to this dentary sport as being 

 not uncommon in some of the Pycnodont genera. The second series 

 (PL III. Fig. 2 h) comprises eight teeth, which, although considerably 

 smaller than the principal grinders, are nevertheless comparatively of 

 larger size than those of Pycnodus toliapicus. They are elliptic in 

 form, differing also in this respect from the oval teeth of that species. 

 The outer row (PL III. Fig. 2 c) contains six teeth very much 

 smaller and nearly circular ; the crown or triturating surface of those 

 not yet come into use is irregularly puckered. It will be gathered 

 from these details that the species is well characterized and broadly 



