THE GREAT FISH-LIZARDS 67 
surface of the sea ; for they have only one pair of fins. But the 
fish-lizards had two pairs of these appendages, and the hinder or 
pelvic pair no doubt were of great service in helping the creatures 
to come up to the surface when necessary. 
These great marine predaceous reptiles literally swarmed in the 
seas of the Lias period, and no doubt devoured immense shoals of 
the fishes of those times, whose numbers were thus to some extent 
kept down. There is the clear proof of this in the fossilised 
droppings — known as '' coprolites,” — which show on examination 
the broken and comminuted remains of the little bony plates of 
ganoid fishes that we know were contemporaries of these reptiles. 
Probably young ones were sometimes devoured too (see p. 72). 
It was in the period of the Lias that fish-lizards attained to 
their greatest development, both in numbers and variety ; and the 
strata of that period have preserved some interesting variations. 
It will be sufficient here to point out two, namely. Ichthyosaurus 
tenuirostris — an elegant little form, in which the jaws, instead of 
being massive and strong, were long and slender like a bird’s 
beak; and also Ichthyosaurus latifrons (Fig. 10), with jaws still 
more birdlike. Our artist has attempted to show the former 
variety in our illustration (Plate IV.). A most perfect example 
of this pretty little Ichthyosaur, from the Lower Lias of Street 
in Somerset, has been presented to the Rational Collection at 
South Kensington by Mr. Alfred Gillett, of Street, and may be 
seen there (Plate III.). In this group of fish-lizards the eyes are 
