AIR-BREATHERS OF THE COAL PERIOD. 271 



The skull seems to have been much of the same form as in Hy- 

 lonomus Lyelli, but very thin and delicate, so that all the speci- 

 mens hitherto found are crushed and fragmentary. The maxil- 

 lary and mandibular bones are furnished with teeth which are 

 bluntly conical in form, and in the latter bone seem to be confined 

 to its front part, or to be very small posteriorly. They are thus 

 much fewer in number than in the species last named. I have 

 been able to make out only 22 in the lower jaw, and they are 

 alternately large and small, as if replaced in this manner as worn 

 out. Their structure is of the same simple character as in the- 

 other species of Hylonomus, and they have large pulp cavities. 



The vertebrae of this species are singular and characteristic. 

 The bodies are elongated and hour-glass shaped, with an internal 

 cavity of the same form filled with calc spar (Fig. 30), and pro- 

 bably once occupied by cartilage. They have, in the dorsal re- 

 gion at least, strong articulating and lateral processes, and were 

 furnished with numerous delicate ribs (Figs. 24, 25, 27). In one 

 of my specimens as many as 38 of these little vertebrae may be 

 seen lying together, and many of them attached to each other. 

 This would indicate that the body was long and slender. It was 

 furnished with limbs, similar to those of H. Lyelli, but very small 

 and slender. The pelvis is of the same expanded form with that 

 of the last species, and a pair of fore feet lying together on one 

 slab, show the remains of four slender toes (Fig. 29). The bones 

 of the limbs are very delicate and thin walled (Fig. 26). The 

 bony scales are oval, and similar to those of the other species of 

 the genus, but very small (Fig. 31.) I suppose it probable that 

 the fragments of skin with imbricated scales represented in Plate 

 V, Figs. 22, 23, and 24, may have belonged to this species, but 

 I cannot certainly affirm that this was the case. 



In length, Hylonomus Wymani could not have exceeded four or 

 five inches, and its form was thin and slender. It may be 

 questioned whether this little creature was not the young of one 

 of the other species. The form of the vertebrae and teeth would, 

 I think, prevent us from supposing that it stood in this rela- 

 tion to H. Lyelli. To H aciedentatus it bears a stronger resem- 

 blance in these respects, though not sufficient to render specific 

 identity probable ; and the occurrence of so many specimens of 

 the smaller species, without any of intermediate size, renders it 

 likely that it did not attain to any greater dimensions. 



Hylonomus Wymani probably fed on insects and larva, and 



