372 THE CARBONIFEROUS SYSTEM. 



SO large and broad as to give the impression that the creature enharged 

 considerably in size toward the posterior extremity of the body, and 

 that it may have been in the habit of sitting erect. The thigh bone 

 is well formed, with a distinct head and trochanter, and the lower 

 extremity flattened and moulded into two articulating surfaces for the 

 tibia and fibula, the fragments of which show that they were much 

 shorter. The toes of the hind feet have been seen only in detached 

 joints. They seem to have been thicker than those of the fore foot. 

 Detached vertebra;, which seem to be caudal, have been found, but 

 the length of the tail is unknown. The limb bones are usually some- 

 what crushed and flattened, especially at their articular extremities, 

 and this seems to have led to the error of supposing that this flattened 

 form was their normal condition; there can be no doubt, however, 

 that it is merely an effect of pressure. The limb bones present in 

 cross section a wall of dense bone with elongated bone-cells, sur- 

 rounding a cavity now filled with brown calc-spar, and originally 

 occupied with cartilage or marrow. Nothing is more remarkable in 

 the skeleton of this creature than the contrast between the perfect and 

 beautiful forms of its bones, and their imperfectly ossified condition, — 

 a circumstance which raises the question whether these specimens may 

 not represent the young of some reptile of larger size. 



The dermal covering of this animal is represented in part by oval 

 bony scales, which are so constantly associated with its bones that I 

 can have no doubt that they belonged to it, being, perhaps, the clothing 

 of its lower or abdominal parts ; while above, it was probably clad in 

 the beautiful scaly covering represented in Fig. 144,* and Avhich shows 

 that the creature, while probably clad with bony scales below, had 

 on its back an array of scaly and spiny ornaments comparable with 

 those of any modern reptile. The bony scales differ in form from 

 those of Dendrerijeton ; they are also much thicker. On the inner 

 side they are concave, with a curved ledge or thickened boi'der at one 

 edge. On the outer side they present concentric lines of growth. 



The only specimens which afford much information as to the general 

 form of Hylonomus Lydli are those represented in Fig. 144. The first 

 is the original specimen from which I described the species in the 



* Description of Fhj. 144. 



(a) Skeleton in matrix, showing jaws, ribs, (/) Bones of foot ; enlarged.' 



vertebras, pelvis, and bones of limbs. (g) Parietal bones, showing foramen; enlarged. 



(6) Portion of skeleton in matrix, showing (h) Vertebra ; enlarged. 



vertebrsB and limb bones. {j) Ribs ; enlarged. 



(c) Portion of maxilla with teeth; enlarged. (i) Bony scale; enlarged. 



(rf) Cross sections of teeth ; enlarged. {I) Portion of scaly cuticle. 



(e) Anterior end of mandible with teeth ; (ra to s) Homy scales, bristles, tubercles, and 

 enlarged. other appendages of the same ; mag. 



