40 GUIDE TO THE FOSSIL REPTILES, AMPHIBIANS, FISHES. 
Wall-cases 
15-17. 
Stands 
A-C. 
Table-cases 
20-23. 
Case H. 
Wall-case 
10 . 
Table-case 
20 . 
Case G. 
tail-fin, which has been seen in a few well-preserved speci¬ 
mens from the German Lias and Lithographic Stone (not 
in the Collection). Both pairs of paddles (Fig. 38) are 
always, present, but the hinder pair is often small. The skin 
must have been quite smooth, without armour, and it is 
shown in some German specimens (not in the Collection) to 
have formed a smooth triangular fin in the middle of the 
back, as in modern porpoises. 
The small Triassic Ichthyosaurs, of which there are no 
specimens in the Museum, suggest that they, like the 
Plesiosaurs, were descended from land animals. In some 
important respects the skull and teeth resemble those of the 
Labyrinthodont Amphibia (p. 47). The Liassic Ichthyo¬ 
saurs, of which a fine series is exhibited in Wall-cases 15, 
16, 17, are typical members of the Order and sometimes 
attain a very large size. The skeleton of Ichthyosaurus 
platyodon, from the Lower Lias of Stockton, Warwickshire, 
presented by Mr. Michael H. Lakin, measures 22 feet in 
length; while vertebrae at the bottom of the same Wall-case 
and skulls in Gallery 3 (pedestals lettered A, B, C) belong 
to much larger individuals. A nearly complete small 
skeleton from the Lower Lias of Street, Somersetshire 
(Plate VI.), is an especially good example of a slender-nosed 
species (Wall-case 15). An equally good specimen of an 
allied species from the Upper Lias of Wurtemberg, at the 
bottom of the same Wall-case, is interesting as showing six 
embryos within the ribs, proving that these reptiles were 
viviparous. Two fragments from the Lower Lias of Barrow- 
on-Soar, Leicestershire (Wall-case 17 and Table-case 21), 
exhibit the fin-membrane round the bones of the fore-paddle. 
Typical Ichthyosaurs seem to have ranged upwards to 
the Chalk, and fragmentary remains of the later species are 
exhibited in Table-case 20. Some of the Upper Jurassic 
genera, however, both in Europe and in North America, are 
almost toothless and have broad paddles, which must have 
been rendered very flexible by a persistent rim of cartilage 
round each of the constituent bones. Ophthalmosaurus is 
a typical and well-known example from the Oxford Clay of 
Peterborough (Table-case 23). 
Coprolites, or pieces of fossilised excrement, are often 
found in the Lias where remains of Plesiosaurs and Ichthyo¬ 
saurs occur, and were probably left by these reptiles. A 
collection is exhibited in Table-case G. They contain 
numerous scales of ganoid fishes which have been eaten, and 
