152 Sir J. W. Bmcson — On Dendrerpeton Acadianum, etc. 



Fig. 4. — Hylonomus Lyelli. Explanation to page 151. 



a. Skeleton in matrix, showing jaws, /. Bones of foot ; enlarged. 



ribs, vertebrae, pelvis, and bones of g. Parietal bones, showing foramen ; enl. 

 limbs. h. Vertebra ; enlarged. 



b. Portion of skeleton in matrix, show- j. Eibs ; enlarged. 



ing vertebrse and limb-bones. k. Bony scale ; enlarged. 



c. Portion of maxilla with teeth ; enl. I. Portion of scaly cuticle. 



d. Cross -sections of teeth ; enlarged. m. to s. Horny scales, bristles, tubercles, 



e. Anterior end of mandible with teeth ; and other appendages of the same ; 



enlarged. magnified. 



Hylonomus Lyelli was an animal of small size. Its skull is about 

 an inch in length, and its whole body, even if, as was likelj'', furnished 

 with a tail, could not have been more than six or seven inches long. 

 No complete example of its skull has been found. The bones 

 appear to have been thin and easily separable ; and even when they 

 remain together, are so much crushed as to render the shape of the 

 skull not easily discernible. They ai-e smooth on the outer surface 

 to the naked eye, and under a lens show only delicate uneven stride 

 and minute dots. They are more dense and hard than those of 

 Dendrerpeton, and the bone-cells are more elongated in form. A 

 specimen in my possession shows the parietal and occipital bones, 

 or the greater part of them, united and retaining their form. We 

 learn from them that the brain-case was rounded, and that there 

 was a parietal foramen. Well-preserved specimens of the maxil- 

 lary and mandibular bones have been obtained. They are smooth, 

 or nearly so, like those of the skull, and are furnished with numerous 

 sharp, conical teeth, anchylosed to the jaw, in a partial groove 

 formed by the outer ridge of the bone. In the anterior part of the 

 lower jaw there is a group of teeth larger than the others. The 

 intermaxillary bone has not been observed. The total number of 

 teeth in each ramus of the lower jaw was about forty, and the 

 number in each maxillary bone about thirty. The teeth are perfectly 

 simple, hollow within, and with very fine radiating tubes of ivory. 

 The vertebras have the bodies cylindrical or hour-glass- shaped, 

 covered with a thin, hard, bony plate, and having within a cavity 

 of the form of two cones attached by the apices. This cavity was 

 completely surrounded by bone, as it is filled with stained calc-spar 

 in the same manner as the cavities of the limb-bones. It was 

 probably occupied with cartilage. The vertebrae were biconcave. 

 The neural spines are short and broad, with zygapophyses, and are 

 not separable from the bodies, the neural arches being perfectly 

 anchylosed to the bodies of the vertebras. There are, on the dorsal 

 vertebras, strong diapophyses or lateral spines, to which the ribs 

 were articulated. The ribs are long, curved, and at the proximal 

 end have a shoulder and neck. They are hollow, with thin, hard, 

 bony walls. There are short ribs which may be cervical. The 

 anterior limb, judging from the fragments procured, seems to have 

 been slender, with long toes, four or possibly five in number. The 

 posterior limb was longer and stronger, and attached to a pelvis so 

 large and broad as to give the impression that the creature enlarged 

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



