i ee 
ON THE CLASSIFICATION OF THE LABYRINTHODONTS. 173 
almost to the base, and plicated on the inner side, while in this species they are 
licated all around like the inner maxillary teeth); (4) the form of the skull, which 
as the orbit larger in proportion, and is also shorter and broader”’*. 
Locality. Coal-measures of South Joggins, Nova Scotia. 
References. Owen, Q. J. Geol. Soc. vol. xviii. p. 242, t. ix. fig. 4, t. x. fig. 3 [1862]. 
—Dawson, ibed. vol. xix. p. 469 [1863]—Jd. Acadian Geology, 2nd edit. 
pp- 362-370, figs. 142, 145 [1867 
Hylonomus, Dawson. 
Teeth (disposition). Maxillary about 30 on each side; mandibular about 40 in 
each ramus; “in the anterior part of the lower jaw there is a group of teeth larger 
than the others” (Dawson). Teeth (structure). Conical, sharp, “perfectly simple, 
hollow within, and with very fine radiating tubes of ivory” (Dawson)t. Cranial 
sculpture, The bones of the skull “are smooth on the outer surface to the naked 
eye, and under a lens show only delicate uneven striz and minute dots” (Dawson). 
Vertebre. Centra elongate, contracted in the middle; some of the superior spinous 
rocesses broad and lofty. Ribs. Long and curved, but some short and straight, 
Pista or notched at the proximal end, hollow. ore limb. “The anterior limb, 
judging from the fragments procured, seems to have been slender, with long toes, 
four or possibly five in number” (Dawson). Hind limb. “The thigh-bone is well 
formed, with a distinct head and trochanter, and the lower extremity flattened and 
moulded into two articulating surfaces for the tibia and fibula, the fragments of 
which show that they were much shorter ; the toes of the hind feet have been seen 
only in detached joints; they seem to have been thicker than those of the fore foot 
....3 the limb-bones present in cross section a wall of dense bone, with elongated 
bone-cells surrounding a cavity now filled with brown cale-spar, and originally 
occupied with cartilage or marrow” (Dawson){. Scutes. The ventral surface 
occupied by oval bony scutes; “the bony scales differ in form from those of Den- 
drerpeton; they are also much thicker; on the inner side they are concave, with a 
curved ledge or thickened border at one edge; on the outer side they present con- 
centric lines of growth” (Dawson): Dr. Dawson has also described an “ ornate appa- 
ratus of horny appendages,”’ which he supposes to have covered H. Lyelli above. 
H. Lyext1, Dawson. 
The description of the genus is that of this, the typical species. 
Measurements (from Dawson’s ‘ Acadian Geology ’). 
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Length of longest rib preserved (chord) .........ecseeeeeeeees 6 
Locality. Coal-measures of South Jogeins, Nova Scotia. 
References. Owen, Q. J. Geol. Soe. vol. cia 238, t. ix. figs, 1-6, 14 [1862].— 
Dawson, tbid. vol. xix. p. 473 [1863].—Jd. Acadian Geology, 2nd, edit. p. 
370, fig. 144 [1867]. 
* Dawson, ‘ Acadian Geology,’ 2nd edit. p. 368. 
+ In Dr. Dawson’s ‘ Air-breathers of the Coal Period’ [1863], p. 61, t. vi. fig. 54, a 
patch of “ palatal”? (vomerine ?) teeth is shown in the centre of the palate and far forward. 
t “All the long bones, even the ribs, are hollow; and the cavity is enclosed by a com- 
pact 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 un- 
changed by ossification in the living species. I conclude, therefore, that these hollow 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.” —O wen, Q. J. Geol. Soo. vol. xviii. p. 238 [1862]. 
