134 



Other formations. Life evidently ex- 

 isted then, for at the close of this in- 

 terval or rather at the beginning of 

 the Silurian we find a large number of 

 Invertebrates. There were corals, 

 crinoids, brachiopods. lamellibranches, 

 gasteropods, cephalopods, worms and 

 crustaceans. All of these animals 

 flourished during the Silurian. 



It was during the latter part of the 

 Silurian that fishes first made their ap- 

 pearance. If they lived earlier than 

 this they were of low organization and 

 possessed no hard parts, and when they 

 died they would entirely decay, leav- 

 ing nothing to be preserved as fossils. 

 Of course, no one lived then to give 

 fishes easy common names, and so we 

 only know them by the long, hard 

 scientific names given by scientific 

 men. These we will use as little as pos- 

 sible in this article. In classifying 

 fishes they fall into a few large groups, 

 as follows : The lowest fish in point of 

 structure is the lancelet, a small, semi- 

 transparent animal, with no hard parts, 

 as teeth, spines or bones. We would 

 not expect it to be preserved as a fos- 

 sil and so we find none. The next 

 group contains our lampreys and 

 hag fishes. TJiese are parasites. 

 They vary in length from a few inches 

 to more than three feet. With a mouth 

 nearly circular they attach themselves 

 to other fishes and feast upon their 

 blood. The hag fish eats its way into 

 the fish and remains there until its host 

 is a living hulk of skin and bones. 

 Fishes known as Pteraspids, thought 

 by some scientists to belong to this 

 group, are found in the upper part of 

 the Silurian. The lampreys of the pres- 

 ent day have no very hard teeth and 

 their backbone is simply very soft 

 cartilage. These ancient lampreys, 

 called Pteraspids, had the head and part 

 of the body covered with a coat of mail. 

 Of these there flourished in the last 

 days of the Silurian quite a number 

 of species. The next group of fishes 

 are the sharks, the most blood-thirsty 

 of all the inhabitants of the sea. Sharks 

 flourished to some extent in the up- 

 per part of the Silurian. The shark 

 has no true bones and its covering 



consists of shagreen tentacles. It is 

 provided with hard teeth and the dorsal 

 fins of the ancient shark were provided 

 each with a hard, stout spine. The 

 teeth were large, flat and fit for 

 crushing. We know these ancient 

 sharks only by the spines, shagreen 

 tentacles and the teeth. These, how- 

 ever, furnished abundant evidence that 

 the sharks in the upper Silurian were 

 numerous as to individuals and species. 

 The Chimera, a fish much resembling 

 the sharks, was also abundant in the 

 upper Silurian. A group of fishes 

 usually known as ganoids and which 

 comprise the lung fishes of the Nile, of 

 Australia, the garpikes of North Amer- 

 ica and the sturgeons, were very abun- 

 dant during the closing days of the 

 vSilurian. The fishes of this group are 

 especially well preserved as fossils, 

 their covering consisted of bony plates 

 or bucklers or of scales covered with a 

 coat of enamel. Their outer covering 

 was well suited to become fossilized, 

 and so we know this group much bet- 

 ter than we do any other found in the 

 Silurian. 



The next and last group of fishes is 

 known as Teleosts, or bony fishes. To 

 this group belong our typical fishes, 

 such as black bass, sun fishes, suckers, 

 cat fishes and the like. None of this 

 group lived during the Silurian. 



Following the Silurian came the De- 

 vonian, which is called the age of 

 fishes. In no time in the world's his- 

 tory have fishes been so large and so 

 abundant as during this age. They 

 outclassed in every respect all other 

 animals. The same general types 

 flourished as those which existed in the 

 latter part of the Silurian. There were 

 more species and more individuals and 

 some grew to an enormous size. 

 Fishes ruled the Devonian seas. The 

 crustaceans, such as trilobites which 

 greatly predominated during the Silu- 

 rian age, diminished greatly during the 

 Devonian. In the struggle for exist- 

 ence they decreased in size and in 

 numbers, and were obliged to seek 

 safety in less favorable places. The 

 Devonian fishes were largely sharks 

 and ganoids, especially the latter. 



