2 The American Geologist. January, i89r> 
its fractures, or 1 may say partly in consequence of them, 
nearly every detail that can be desired is here displayed in 
more or less perfection in one part or another of the slab. 
Owing to this wonderful condition, it has proved possible to 
reproduce the dentition in almost its original perfection and 
thus to demonstrate the resemblance, and the difference, be- 
tween this long extinct genus and the sharks of our present 
sea, so far as the teeth are concerned. 
Plate I shows the head of Cladodus darh-i as it lies on the 
slab, belly upwards. The cartilages have left distinct im- 
pressions of the head, enabling us to trace them as truly as 
we could trace the general outline in the earlier specimen. In 
reproducing it for our figure, little has been attempted in res- 
toration beyond supplying from each side what is lacking on 
the other or filling manifest gapsin the continuous cartilages, 
as for example in the gill-arches. 
The excessive bluntness of the snout, which is so conspicu- 
ous in a shark, may possibly be in part due to the destruction 
by decay of a small anterior portion before fossilization. But 
the defect here, if real, is very slight, and beyond doubt the 
muzzle of this species was more nearly square than it was 
represented in our earlier figure. Its sharpness was doubtless 
greater in a horizontal direction, as is the case with most of 
the recent sharks. 
The form of the nasal capsules is strikingly like that of 
some of the existing species. They give the conspicuous 
rounded outline to the front of the head and exhibit the same 
immense development of the olfactory lobes of the brain (rhi- 
nencephalon) as we find at the present day. They lie just in 
front of and below the orbits, and though crushed they do not 
appear to have been at all flattened out or widened during 
fossilization. 
The Eyes. . The left orbit is well preserved and shows the 
dermal radiating plates of the upper side of the eye, which in 
the fossil are somewhat displaced. Those of the lower side 
are concealed beneath the cranial cartilages. The right orbit 
retains more correctly its position in life, and for that reason 
it shows less of its structure, being more difficult to clear from 
the stone. Evidently the position of the eye was nearer to 
the front of the head than is now the case, except in certain 
