612 BRITISH PALZEOZOIC FOSSILS. [ Pisces. 
This species is strongly distinguished from the &. Hibberti by the remarkable slenderness of the dentary 
bone, and the slenderness of the teeth, or small proportion which the width of the base bears to their length. 
Position and Locality.—V ery rare in the carboniferous shales of Gilmerton. 
Explanation of Figures —P\. 3. G. fig. 17, dentary bone and teeth, natural size (wanting a little of the 
posterior end); the letters a, 6, and c, mark the apparent places of the posterior laniary teeth. 
Ruizopus Hipperti (A4¢.) 
Ref. and Syn.= Megalichthys Hibberti Ag. and Hibbert Trans. Roy. Soc. Edinb. (1836) Vol. XIII. p. 202. 
t. 8. f. 1,2. t. 9. f. 2, 3, 9, 10. fig. on page 183 = Holoptychius Hibberti Ag. (name). Poiss. Foss. ; ? = Ho- 
loptychius Portlocki Ag. Portk. Geol. Rep. t. 13. f. 5 to 11. 
Desc.—General form unknown, (but supposed to resemble that of Holoptychius). Dentary bone in mode- 
rate-sized individuals about fifteen inches long, and about three inches deep at the third laniary tooth; 
apparently five laniary teeth on each dentary bone, irregular in size, the anterior one much larger than the 
rest, and the posterior one smallest ; the distance between the laniary teeth either a little more or less than 
their own length, but irregular; each laniary tooth is nearly straight, having an elliptical section, leaving a 
cutting anterior and posterior edge; the distal two-thirds of each tooth smooth, the basal exposed portions 
varying from one-fourth to one-third, the length of the exposed part coarsely plicated longitudinally ; between 
the laniary teeth very numerous irregular ones of the same structure, varying from one-fifth to one-half the 
length of the adjoining laniary ones, having a rather shorter proportion of the base plicated; average width 
of the base varying from rather more than one-third to two-fifths the length of the tooth, but varying slightly 
and irregularly in different parts of the mouth of the same specimen; laniary teeth set in deep cylindrical 
sockets, about two-thirds the length of the exposed portions. Surface of the jaw-bones covered with a small, 
close, vermicular tuberculation, averaging five to seven tubercles in three lines. In the above dentary bone the 
anterior laniary tooth is about three inches in length above the edge of the socket, the width of base being 
about thirteen lines, about ten lines of the base is longitudinally plicated, the plicze being about one line 
wide; a fracture shews the cylindrical base of the same tooth fourteen lines in diameter at two inches in 
depth, strongly distinguished from the surrounding mass of bone in colour, of a moderately coarse cancellous 
texture, with the pulp-cavity obsolete. The average length of the following intermediary teeth is half an inch ; 
owing to a fracture the size of the second laniary tooth is uncertain, but the third one is about two inches 
long; immediately preceding intermediary teeth being about five lines long, the fourth, or last laniary tooth, 
is rather less than one inch long; between it and the third are two half-grown laniary teeth at irregular dis- 
tances. Internal structure: a vertical section shews a conical, moderately large pulp-cavity in the centre of 
the smooth portion of the tooth, increasing in width as far down as the commencement of the external 
plicee of the surface, which latter indicate externally so many inflections of the substance of the tooth, 
impinging on the pulp-cavity, and dividing it first into vertical radiating fissures, which ultimately are reduced 
into numerous medullary canals, blending at last with the general, small, subuniform cancellous structure of 
the root near the base of the socket; a transverse section of the smooth part of the tooth shews a central 
round pulp-cavity, from which the fine dentine tubes radiate to the surface, where they are covered by a thin 
layer of ganoine; lower down through the plicated portion the central pulp-cavity is broken up as before 
described : first laniary tooth of other specimens four inches seven lines long, and one inch eight lines wide at 
base, about two-fifths of the length longitudinally plicated. Scales rotundato-subtrigonal, bony, rather thin, 
varying from nine lines to five inches in diameter, (the large scales proportionally thinner than the small ones) ; 
inner surface nearly smooth, with obtuse concentric lines of growth, and a small, flattened, prominent, ovate 
boss of attachment, slightly excentric towards the base of the scale, and sometimes with a very few, smaller, 
scattered granules (? from disease) ; intimate structure shewing an extremely minute reticulation (as in Gilyp- 
tolepis) ; about nine of the reticulations in one line barely visible to the naked eye, but most distinct on the 
part of the scales overlapped by the others; exposed portions of each scale (about two-thirds of its surface) 
entirely covered with a very close vermicular tuberculation ; about five of these granules in the space of one line. 
