238 PROCEEDINGS OF THE GEOLOaiCAL SOCIETY. [-^W- 2, 



2. Description of Specimens of Fossil Reptilia discovered in the 



COAL-MEASUEES of the SoUTH JOGGINS, NoVA ScOTIA, hy Dr. J. W. 



Dawson, P.G.S., &c. By Professor Owen, F.R.S., P.G.S. 

 [Plates IX. & X.] 

 ■The following specimens were transmitted to the Museum of the 

 Geological Society by Dr. Dawson, in a series of boxes and parcels, 

 most of which are numbered according to a list accompanying them, 

 and have been submitted, by his desire, to my inspection. The 

 descriptions will follow in the order of that list. 



"Box No. 1. — Hylonomus Lyelli, Dawson." 



This specimen is imbedded in a portion of a thin layer of carbo- 

 naceous matter, measuring six inches by four inches. It consists of 

 scattered parts and impressions of vertebrae, ribs, limb-bones, and part 

 of a cranium crushed, including part of a maxillary bone with teeth 

 (PI. IX. figs. 1-5). Not any of the bones are entire : all the long bones, 

 even the ribs, are hollow; and the cavity is enclosed by a compact wall 

 of almost uniform thinness throughout each bone, indicative that 

 such cavity was not properly a medullary one, in the sense of having 

 been excavated by absorption after complete consolidation of the bone 

 by the ossifying process, but was posthumous, and due to the solution 

 of the primitive cartilaginous mould of the bone, which had remained 

 unchanged by ossification in the living species. I conclude, there- 

 fore, that these hoUow long bones (and, indeed, the bodies of the 

 vertebrae seem only to have received a partial and superficial crust 

 of bone) were originally solid, and composed, like the bones in most 

 Batrachia, especially the Perennibranchiates, of an external osseous 

 crust, enclosing solid cartilage. The body of the vertebra (figs. 1 & 2) 

 is chiefly represented by a downward growth of the base of the neural 

 arch (n) ; and in the best-preserved specimen there seems to be a 

 distinct inferior plate (c), with a median longitudinal channel on the 

 lower surface, — such vertebrae belonging to the dorsal region : the 

 cylindrical cavity of the centrum was doubtless occupied by the noto- 

 chord. The neural arch developes a short, broad diapophysis {d), to 

 which the rib articulates : it also has zygapophyses both before {z) 

 and behind (z'), and a moderately long truncate spine (n s), slightly 

 expanding in the fore-and-aft direction to its summit. The ribs are 

 of various lengths, the shorter ones straight, the longer ones slightly 

 bent ; the best-preserved of these have an expanded end, slightly 

 notched (fig. 3), but none show a distinctly bifurcate extremity. 

 Those limb-bones, metapodials or phalanges, which have their arti- 

 cular end preserved, show it to be flattened (fig. 4), — not fashioned 

 for a condyloid or trochlear joint with articular cartilage and syno- 

 vial membrane, but adapted for a simple ligamentous union, as in 

 the digits of the Salamanders, Turtles, Amphiume, and Proteus. One 

 end of some of these bones shows a short longitudinal impression at 

 the middle. The surface of some of the larger long bones shows 

 longitudinal striation, indicative of a fibrous structure like that of 

 the bones in some fishes. The maxillary fragment in the slab, 



