306 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 19, 
and middle lateral plates were united by their corresponding margins.” 
The specimen from which this description was taken is now before me, | 
and shows, in fact, not the under surface of the fish, but the side view ; 
and has enabled me, with the assistance of two other specimens from 
Gamrie, to decipher the relations of the plates protecting this part 
of Pterichthys. 'The lateral plates of the flat surface (fig. 2, e, e, f, f) 
to which I have alluded appear to have been reflected at right angles, 
and to have extended along the side of the fish until meeting the 
lateral plates of the opposite side (fig. 1, c, d). In consequence of 
this form they are frequently crushed and mutilated, and it is only 
after a careful examination of a great number of specimens that I 
have convinced myself that the appearances frequently seen of divi- 
sion along the line of the angle are not due to natural sutures, but to 
accidental fracture. All the component plates of the carapace, with 
the exception of the lozenge-shaped plate g, are united by simple 
sutures ; this on the contrary is attached to its neighbours by broad 
Squamous sutures, the lateral bones overlapping its margins on all 
sides. Consequently this bone when seen from the inside occupies 
nearly twice the area of its external visible surface, a fact which re- 
quires to be borne in mind when seeking for specific characters. It 
is difficult without restorations to convey a clear idea of this compli- 
cated arrangement of parts composing the bony envelope of the | 
Pterichthys. The contour must have had considerable resemblance 
to a high-backed tortoise, with the carapace culminatmg near the 
anterior margin ; thus a transverse section through the umbo would 
be not unlike the outline of a stirrup-iron, or the head of a Gothic 
arch of the decorated period; a longitudinal section would more 
resemble the section of a Parmophorus or any Patelliform shell with 
an excentric apex. The question now arises, whether the helmet- 
shaped plate and its associates, or the lozenge-formed plate and its 
collaterals, constituted the back of the Pterichthys? And first we 
will consider the adaptation of the form and anatomical structure of 
the being to its presumed habits and mode of life; for it is a law 
without exception, save where human presumption has dared, in its 
ignorance, to arraign the all-wise designs of the Omnipotent,—a law 
based immoveably on the study and contemplation of the Creator’s 
works by the wisest and most gifted mortals who have so exercised 
their talents,—a law receivmg day by day more emphasis as our 
limited knowledge extends into new regions of investigation,—that 
the organization of living structures is ordained with special reference 
to the conditions under which they are destined to exist*. If then 
the habits of Pterichthys required it to float and sail on the surface 
of the ocean, the ridge-formed surface would be well-adapted, like 
the keel of a boat or the sternum of a gull, to cleave the waves as 
well as adjust the equilibrium of the body. But the density of the 
tegumentary investment, and the entire organization of the animal, 
forbid such a supposition. Nor is it probuble that a fish all but 
destitute of fins, and of great specific gravity, could have frequented 
* See Ray, Paley, Buckland’s ‘ Bridgewater Treatise,’ passim. 
