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). 



FIG. 10. Skull of Ichthyosaurus latifrons. 



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 National 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 



