170 AIR-BREATHERS OF THE COAL PERIOD. 



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 described in the last sec- 

 tion. The bony scales are represented magnified in Plate V. figs. 

 19. 20, and 21. It will be seen that they differ in form from those 

 of Dendrerpeton ; they are also much thicker. On the inner side 

 they are concave, with a curved ledge or thickened border 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 Lyelli are those represented in Plate 

 V, figs. 1 and 9. The first is the original specimen, from which 

 I described the species in the paper already referred to. The 

 bones, being small and of dark colour, are not very conspicuous, 

 and many of them are broken, but many are beautifully perfect ; 

 and even those which are removed have left very distinct moulds 

 of their form in the fine-grained matrix. In the figure I have 

 carefully traced their outlines in their natural position, with the ex- 

 ception of the maxillary bone and mandible, which are removed 

 from their place in the matrix, to bring the whole into a more com- 

 pact form. The specimen also shows, in addition to the bones 

 delineated, many fragments of the skull and scapular bones, crushed 

 in such a manner that their forms cannot be distinguished. The 

 specimen shows remains of thirty vertebrae, of which four appear 

 to belong to the neck, and the rest are probably nearly all dorsal 

 and lumbar. Three of the most perfect are represented enlarged, 

 in figs. 15 and 16. Of about twenty ribs, more or less complete 

 fragments remain. The fore limb is represented only by the im- 

 pression of a humerus, (e), but other bones which may have 

 belonged to it are scattered elsewhere on the stone. The pelvis, (i) 

 is nearly entire,^though crushed and flattened. One thigh bone 

 remains tolerably perfect, and beside it lie the tibia and a part of 

 the fibula, with several bones of the foot. The dimensions of these 

 parts are as follows : — 



Length of maxillary 0.7 inch. 



" mandible 0.7 " 



" longest rib, (chord) . 0.6 " 



" humerus 0.5 " 



