Pisces. | UPPER PALZOZOIC VERTEBRATA. 611 
CENTRODUS sTRIATULUS (M/"Coy). Pl. 3. G. fig. 1. 
Ref.—Id, M°Coy, Ann, and Mag. Nat. Hist. 2nd Series, Vol. IT. 
Dese.—Tooth about seven lines long and one and half line in diameter at base; conical, gradually 
tapering to the pointed apex, with a slight backward curve; about one-fifth of the surface towards the apex 
perfectly smooth ; the remainder, under the lens, is minutely and irregularly striated longitudinally. 
This remarkable tooth, the only species I as yet know of the genus, seems to present (as far as yet 
known) all the characters, external and miscroscopic, of a true Saurian reptile. 
Position and Locality —Common in the bituminous carboniferous shale of Carluke, Lanarkshire*. 
Explanation of Figures.—P\. 3. G. fig. 1, perfect tooth, natural size, on lower corner of matrix; on 
upper end, a rough section of a smaller tooth shews the great size of the pulp-cavity and its width at base. 
From the carboniferous shale of Carluke. Fig. 1 a, magnified view of the lower tooth of fig. 1. Fig. 1 4, 
section of base of last specimen, shewing the great size there of the pulp-cavity; fig. 1c, section of ditto at 
one-third the length from the apex; fig. 1 d, portion of last section, highly magnified as a transparent object, 
shewing portion of central pulp-cavity, the dentine tubes, calcigerous cells, and ? enamel layer of surface. 
5th Family. CQCZLACANTHI. (See page 589.) 
Genus. RHIZODUS (Ow.) 
The fishes of this genus are very imperfectly known, but the premandibular bones have been described 
by Prof. Owen in his Odontography, and the structure of the accompanying teeth gave rise to his generic 
name Lhizodus for the Holoptychius Hibberti of Agassiz list. The teeth differ from Holoptychius in being 
very unequal in size, having three to five very large laniary teeth on each side in each jaw, with numerous 
smaller ones, and in having an elliptical (instead of round) section, with sharp cutting edges. Like Holo- 
ptychius, all the teeth are fluted near the base, and are set in deep cylindrical hollows in the jaws. The internal 
structure presents a small central pulp-cavity in the smooth part of the tooth, but which splits up into a 
number of vertical slits at the lower suleated part, one corresponding to each of the external sulci, as in the 
Labyrinthoid types, the sides giving off dentine tubes at right angles; these slits with their folds of dentine 
are separated below by intrusions of osteo-dentine, with bone-cells, and finally they become broken up into root- 
like canals, blending with the cancellous bony structure of the bottom of the sockets. The scales are very 
large, rather thin, rotundato-quadrate or subtrigonal, deeply imbricating as in Holoptychius, but thinner, and 
with a minutely reticular internal structure; the under surface is nearly smooth, with a few concentric lines of 
growth, and an ovate, flattened articular tubercle, a short distance from the middle. 
Ruizopus GRacinis (AZ°Coy). Pl. 3. G. fig. 17. 
Desc.—Dentary bone about eleven and half inches long, and only one inch four lines in greatest depth ; 
surface of the bone covered with a close, obtuse, small tuberculation (about four tubercles in three lines). 
Apparently four laniary teeth in each dentary bone (but only the anterior one distinctly known); all the teeth 
much more slender than in the R. Hibberti. First laniary tooth slightly arched backwards, sharp-edged, 
width only one-fourth of the length (length above the bone one inch nine lines, width at base five lines, length 
of plicated portion three to four lines) ; the socket for the second laniary tooth is about the length of the first 
one behind it, with eight intermediary teeth resembling the large ones, but only about three to six lines long 
irregularly ; from eight to eleven similar teeth are behind the apparent place of the other laniary teeth, which 
are broken off in our specimen. 
* This is also the locality of the first observed example of a true carboniferous Reptile in British Rocks—the 
Parabatrachus Colei (Ow.), the Reptilian characters of which, and aflinity to the Reptiles of the German coal-measures, I 
had the pleasure of first pointing out in the collection of Lord Enniskillen, at Florence Court; those yiews were subse- 
quently acquiesced in by Professor Owen, and illustrated in his paper in the Quarterly Journal of the Geological Society 
of London. 
