Among the Trigonia will be found a vast variety of the most symmetrical forms, most of which are elegantly ornamented.
Fig. 14.
The two representations which we have given of the Trigonia scabra ([Fig. 14] and [15]) will convey a general idea of the more striking characteristics of this class of fossils, which are found distributed abundantly over the Portland rocks. The manner in which the folds of the shells overlap each other is singular, and gives to them often a very striking resemblance to the foldings of leaves in the leaf-bud of plants. The curved lines, formed by the small bosses regularly elevated from the striæ, running transversely to these lines in many species, give an exceedingly pleasing outline, which certainly adapts these Trigonia, from the variety of forms thus produced, to the purposes of the art-manufacturer in a peculiar manner.
Fig. 15.
By the wonderful transmutation of organic structures, by those natural processes
“Which turned the ocean-bed to rock,
And changed its myriad living swarms
To the marble’s veined forms,”