TR1LOBITES AND OTHER FOSSIL CRUSTACEA. 187 



same at the time when crustaceans endowed with the 

 faculty of vision were first placed at the bottom of 

 the primeval seas, as at the present moment." 



That the Trilobites were bottom-feeders and 

 haunters, there can be little doubt. The late Mr. 

 Salter, than whom no geologist was better acquainted 

 with Trilobites, was of opinion that they not only 

 lived there, but fed on the organic mud, something 

 after the manner of earth-worms. The simple struc- 

 ture of their mouths, and the absence of antenncs or 

 feelers, indicate such a habit. 



My readers will have seen from the illustrations 

 the strong external resemblances between the earliest 

 king-crabs, such as the Belinurus, and one genus of 

 Silurian Trilobites (Trinucleiis}. The chief apparent 

 difference is in the ends of their bodies, that of the 

 king-crab being prolonged into the dart shape which 

 gives to it its generic name, whilst in the Trinucleus 

 it is round. But we have only to glance at figures 

 of various kinds of Trilobites to see that they vary 

 amongst themselves in this respect. Thus in Asaphus 

 cattdatus (Fig. 139), one of the commonest of Lower 

 Silurian Trilobites, we have the pygidium, or tail, 

 drawn into a point. 



Undoubtedly the Trinucleus (\g. 146) is one of the 

 prettiest of Trilobites. It has a look which suggests 

 the mysterious Egyptian figures of ancient courtiers ! 

 The head or cephalic shield is much developed, and 

 on each side is prolonged into two spines half as long 



