Pisczs. UPPER PALAOZOIC VERTEBRATA. 621 
portion of the crown is crossed by seven transverse imbricating ridges in a space of four lines, the posterior ones 
are three-fourths of a line apart, and have a double curvature arising from a small backward wave in the middle, 
the anterior ones are closer, and pass with a slight forward curve across the tooth; all the imbrications have a 
backward curve at their extremities, giving them the appearance of lapping round the crown, and all have their 
free edges directed backwards, so as to resemble a row of Petalodi or other shark’s teeth soldered together in 
the position they usually occupy, one behind the other; the posterior half is without ridges, the whole crown is 
slightly convex at the sides and concave in the middle ; the surface is dull, and seen by the lens to be finely 
punctured. 
Position and Locality.—Rare in the dark impure limestone overlying the main carboniferous limestone of 
Derbyshire. 
Explanation of Figures.—P1, 3.G. fig. 5, natural size; fig. 5 a, portion of surface of ditto magnified. 
Genus. COCHLIODUS (A¥.) 
Gen. Char—Lower jaw thick, short, bony, V-shaped, bearing on each ramus two obliquely twisted and 
obtusely ridged semicylindrical teeth, strongly inrolled on the outer margin, convex above, concave below, with 
porous grinding surfaces as in Psammodus, from the termination of the vertical medullary canals (young teeth 
replacing the old vertically as in the Pycnodonts). 
The general form of the teeth on a perfect jaw found by Capt. Jones, and the cast of which was examined 
and figured by Profs. Agassiz and Owen, recalled in their opinion the arrangement in Cestracion ; but an almost 
equally perfect specimen presented by Mr Stokes, of Caius College, to the collection, enables me to state that 
there can be no real affinity with Cestracion or any of the sharks; for, first, the teeth are supported on a strong 
bony jaw as in Placodus (which also agrees in having three teeth on each side of the lower jaw, although differ- 
ing in microscopic structure) ; secondly, the inrollment of the teeth is on the outside of the jaw, and not as in 
sharks on the inside to allow the succession of teeth from behind forwards; and finally, a broken tooth of 
another species, the CO. oblongus, also given by Mr Stokes, enables me to prove the succession of the teeth was 
not by revolution from behind as in the Plagiostomous fishes, but vertically from below upwards, as in the Pyc- 
nodonts. See our Plates, 3. H. fig. 19, and 3. I. fig. 28. 
The genus is confined to the carboniferous rocks. 
CocHLiopUS AcuTUS (Ag. name only). Pl. 3. I. fig. 24. 
Dese.—Posterior tooth oblong, obliquely attenuated behind at an angle of about 65°; anterior edge sloped 
backwards and inwards at about 60°; surface with three very strongly marked, oblique ridges, separated by 
deep concayities ; the first ridge most prominent, narrow, acutely angulated, coinciding with the anterior edge, 
which is very steeply sloped, usually separated from the adjoining concavity by an obscure narrow sulcus ; 
middle ridge much broader, and placed rather behind the middle of the tooth, sloping gradually towards the 
base of the anterior ridge, but abruptly rounded into the deeper and narrower concavity, which separates it 
from the posterior marginal ridge, which is prominent, narrow, and rounded, forming the posterior point of the 
tooth. Middle tooth unknown. Anterior tooth small, triangular, marked with three narrow, prominent, very 
oblique ridges, the first coinciding with the posterior margin, and forming an angle of 50° with the outer edge, 
the anterior part of which forms the third ridge; the secondary ridge is more obtuse than the other two, and 
a little on the posterior side of the middle, the intervening spaces deep, concave. Entire surface minutely 
granulo-punctate by the extremities of the vascular canals (averaging eight in one line), covered in some places 
with a very thin layer of ganoine. Average length of posterior tooth one inch two lines, width at anterior 
margin eight lines, length of anterior tooth seven lines, width of posterior margin six lines. 
This species is distinguished from the others by the strongly-pronounced oblique ridges, and their approach 
to angularity, which is most distinct in the anterior ridge of the posterior tooth, which ridge is also remarkable 
for being more prominent than the middle one in that tooth. There are one or two marginal sulci round both 
the interior and the obliquely inrolled exterior edges. It is only by some misunderstanding that Capt. Jones is 
