LAND ANIMALS OF THE COAL PERIOD. 



377 



lower jaw, wliich show that a few teeth there also were larger than 

 the otliers, but whether they dlffei'ed in form cannot be determined. 

 The j^ulp cavity of the teeth is less extensive in proportion than in //. 

 Lyelli^ and the structure in the cross section is simple, showing merely 

 radiating ivory tubes. 



Fig. 145. — Hylononius aciedentatus, Dawson. 



WWW^Ke?5Qr°P 



liiiliiJlbmiPiM^^ 



l- 



(a) Maxillary bone; enlarged. 



(b) Mandible; enlarged. 



(c) Teeth ; magnified, showing front and side 



view of ordinary tooth and grooved 

 anterior tooth. 



(d) Section of tooth ; magnified. 



(e) Scale ; natural size and magnified. 

 (/) Pelvic bone (?); natural size. 



(ff) Rib ; natural size. 



(?i) Scapular bone (?); natural size. 



(i) Palate; natural size. 



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

 certain inference as to its form. Its vertebra} would seem to have 

 resembled those of //. Lyelli, but to liave been elongated and more 

 thoroughly ossified. Its ribs are similar in form and proportion to 

 those of the last-named species. A pelvic bone and some detached 

 phalangial bones, as well as very fragmentary limb bones, Avould 

 indicate that its limbs were well developed. Its external scales are 

 similar to those of the last species, but larger, and a few fragments of 

 skin show scales and appendages similar to those of //. Lydli, but of 

 greater dimensions. The microscopic structure of its bone is also 



2 B 



