638 
DR. J. W. DAWSON ON ERECT TREES CONTAINING ANIMAL 
in 1 millimetre; anterior mandibular teeth, somewhat larger than the others, and bent 
or hooked. Vomer or palate with minute teeth. Thoracic plate large. Scales of 
abdomen oval, but somewhat narrow, and tending to be oat-shaped. 
Length of mandible (imperfect) 
,, humerus . 
„ vertebra .... 
„ tibia 
,, thoracic plate . 
,, six caudal vertebrae 
9 millimetres. 
1*5 centimetre. 
8 millimetres. 
5. Smilerpeton aciedentatum, Dawson (Plate 40, figs. 28 to 45). 
\Hylonomus ciciedentatus, Dn., Journal of Geological Society, l.c. ‘Air-breathers of 
the Coal Period/ p. 49. ‘Acadian Geology/ p. 376.] 
This animal was originally referred by me to the genus Hylonomus; but additional 
specimens and more careful comparison oblige me to place it in a new genus. 
Its most remarkable distinction is the form of the mandibular and maxillary teeth, 
which are of a peculiar wedge-shape, being broad and oval at base and narrowed to a 
longitudinal edge at top. Thus, when viewed from the side they appear narrow and 
blunt, but when the jaw is broken across, and they are viewed from the rear or front, 
they appear broad and sharp-edged. The effect of this arrangement is that the jaw is 
armed with a closely-placed series of chisels or wedges, giving an almost continuous 
edge. At the end of the mandible some of the teeth are longer and more conical. 
Another important character is that the palatal and vomerine bones seem to have 
bristled with teeth, mostly of very small size ; but there are also some larger palatal 
teeth, of which some are sharply pointed and others blunt with furrowed points. 
The vertebrae are of the same type with those of Hylonomus; but some which appear 
to be caudal have a pointed spine above, indicating perhaps a flattened tail. The ribs 
are short and stout. 
Only a few fragments of the limbs have been found ; they would seem to have been 
less developed than in Hylonomus, and perhaps this animal was less gifted 'with 
powers of walking on land than any of the other Microsauria. This would accord 
with the fact that its bones are much scattered, and occur chiefly in sandy layers, as if 
introduced in times of rain or of partial inundation. 
Some fragments indicate thoracic plates, and there are numerous abdominal scales of 
oval form. Above, the body appears to have been clothed with small tubercles and 
horny scales, and to have had cuticular pendants like those of Dendrerpeton. 
In a large specimen the mandible measures 2’2 centimetres, the femur 2 centimetres, 
and a rib the same. The following are measurements from a smaller specimen :— 
