AIR-BREATHERS OF THE COAL PERIOD. 269 



which the two first arc magnified slightly, the last natural size.* 

 Since the publication of ray previous paper, I have ascertained 

 that the intermaxillary bones bore teeth of the lorm represented 

 in Fio-. 6. They ate larger than the others, thick and coming to 

 a blunt point, which is seamed with longitudinal and slightly 

 spiral ridges. This singular tooth must have been a most effi- 

 cient instrument for crushing and penetrating the coats of crusta- 

 ceans and insects, or the bony armour of the smaller ganoid fishes. 

 Remains exist at the extremity of the lower jaw, which show that 

 a few teeth there also were larger than the others, but whether 

 they differed in form cannot be determined. The pulp cavity of 

 the teeth is less extensive in proportion than in H. Lyelli, and the 

 structure in the cross section is simple, showing merely radiating 

 ivory tubes, as in Fig. 7. The bone represented in Fig. 8, was 

 found with these remains, and as it is too large for the last spe- 

 cies, - and different from anything known in Dendrerjieton, it pro- 

 bably belongs to the creature now under consideration. It is thin 

 and smooth, except at the upper margin, where it has in the 

 centre a group of small conical teeth. It evidently belongs to 

 the palate, and somewhat resembles the palatal bone of Meno- 

 branchus, but is broader, and the latter has no teeth. ■ Detached 

 fragments of the skull show that its bones were thin and dense, 

 and smooth on the surface as in H. Lyelli. That represented in 

 Fig. 9 would seem to be a frontal bone seen from the inside. 



The remains of H. aciedentatus are too scanty to warrant much 

 certain inference as to its form. Its vertebrse would seem ■ to 

 have resembled those of II Lyelli, but to have been elongated 

 and more thoroughly ossified (Fig. 16). Its ribs are similar in 

 form and proportion to those of the last named species (Figs. 10 

 and 11). A pelvic bone and some detached phalangial bones 

 (Figs. 12 and 13) as well as very fragmentary limb bones, would 

 indicate that its limbs were well developed. Its external scales 

 are similar to those of the last species but larger, and a few frag- 

 ments of skin show scales and appendages similar to those of H. 

 Lyelli, but of greater dimensions (Figs. 15 and 62). The micros- 

 copic structure of its bone is also similar to that in the last species 

 (Fig. IV). No doubt a more perfect specimen would show many 

 points of difference between these species, not now appreciable ; 



* In Prof. Owen's paper, J.G-.S., Vol. 18, this bone is figured, but in- 

 correctly stated to be twice natural size, and referred to H. Lyelli. 



