240 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 2, 



increase from the pointed end of the bone to about the tenth tooth, 

 and thence continue with little difference of size : the crown ex- 

 pands slightly beyond the implanted base, before narrowing to the 

 rather blunt-pointed end. The outer surface of the jaw-bone shows 

 a striated or strio -punctate pattern of sculpture. 

 • A fourth portion (5 h) included parts of the bones of a short 

 natatory fore limb (PL IX. fig. 10). The humerus (h) has an 

 expanded proximal end, with three ridges, two of them more extended 

 than the other ; the shaft of the bone is rather bent. This bone has 

 been dislocated from the radius (r) and ulna (n), beyond which are 

 evidences of three, if not four, digits ; these progressively increase 

 in length to the fourth (iv), of which, and of the third, impressions 

 and parts of three successive phalanges are shown. These are 

 slightly expanded at their flattened articular ends, at which the 

 longitudinal impressions may be seen in two instances; but the 

 joints were syndesmotic, as in Archegosaurus and modern aquatic 

 batrachian reptiles ; and the humerus and antebrachium are short in 

 proportion to the manus, although not to such a degree as in Arche- 

 gosaurus. 



The group of dermal scutes includes some (PI. IX. fig. 13 6,c) which 

 are nearly perfect, of an oval form, smooth on the inner surface, with 

 a low longitudinal ridge, half the length of the scute, on the outer 

 surface ; the external layer is of ganoid hardness ; the internal struc- 

 ture is cellular. They indicate the nature of the covering of one of 

 the species of Hylonomus. 



'•' Box Wo. 3. — Hylonomus Wymanni, Dawson." 



The remains of foot-bones (PI. IX. fig. 11) in one of the portions of 

 coal- shale in this box show a tridactyle structure, with more slender 

 proportions than in the Hylonomus aciedentafus ; but the phalanges 

 have the same flat joints and incomplete ossification, a thin external 

 crust of bone enclosing a cavity which had been occupied by cartilage : 

 they much resemble the phalanges of the Axolotl. 



A second portion contains a series of six or seven crushed neural 

 arches of vertebrae (PL IX. fig. 12), of a length twice their breadth, 

 with horizontal zygapophyses — the spines probably broken away. In 

 the proportion of length to breadth, these vertebrae resemble those of 

 Proteus*. There is no evidence of an ossified centrum in any part 

 of this series ; but there are some elongated vacuities, which seem 

 to represent the unossified parts of centrums, partially cased by thin 

 bone. The impressions, with filmy remains of bones of a second 

 series of six vertebrae, of similar slender proportions, are preserved 

 in the same portion of coal. 



PL IX. fig. 13 a represents one of the largest specimens of a rib, 

 partly in bone, partly in impression, with an expanded, slightly 

 notched head, as in the ribs of the Axolotl, but of greater length and 

 more curved than in any modern naked Batrachian : it is hollow, as 

 in the shorter specimens, with a thin outer crust. 



* Ciivier, Ossemens Fossiles, v. pt. ii. pi. xxvii. fig. 14. 



