62 



HARDWICKE'S SCIENCE-GOSSIP. 



some it appears to have been very thin, in others 

 harder. As a nile, it was chitinous, after the manner 

 of tlie elytra: of beetles, altliough there can be no 

 doubt this was often strengthened by the presence of 

 hmy matter. In the carboniferous Trilobites {Phil- 

 lipsia, &c. ) the carapace seems to have contained 

 more limy matter in its composition than other species. 

 In this genus we always find the moultings in 

 the two parts of body and tail, and head. In the 

 Calymenes (fig. 14) the thoracic or ringed part is 

 frequently found by itself, and not seldom the rings 

 are detached, as if the whole mechanism of the coat- 

 of-mail-like armour had become loosened and got 

 scattered about. Undoubtedly the chemical composi- 

 tion of the carapace differed accordingly as the habits 

 of the Trilobites varied. 



The Cambrian Trilobites, as a rule, differ from their 



Fig. 55. Trimtclcus 

 L loydii. 



Fig. 54. Head-shield and Caudal 

 shield of Phillipsia. 



Silurian descendants and representatives in having a 

 larger number of rings or segments to the thoracic (or 

 middle) part of the body. The tail part (caudal 

 shield) is, however, less developed than in the Silu- 

 rian species. The side-lobes of some genera, Pat-a- 

 doxidcs and Acidaspis, are fringed, and, in the case of 

 the latter, further adorned with spines. Some of 

 these may have been sexual distinctions, although we 

 are now forced to regard them as specific. Dean 

 Buckland and many other naturalists have regarded 

 an isopod crustacean abundant in the seas around 

 Tierra del Fuego and the Straits of Magellan, as 

 being nearly allied to this group of Trilobites. This 

 crustacean is called Serolis. Its cephalic shield has 

 compound sessile eyes, arranged in halfmoon-shaped 

 lobes exactly like those of some Trilobites. The 

 segments or joints of the thoracic portion of the body 

 are fringed, as in Faradoxides, and there is a movable 

 caudal or tail shield, as in Phacops catidatus, an 

 abundant Silurian Trilobite. Only the antennae and 

 mouth-organs differentiate them. But these are very 

 thin and weak, and after death may soon be detached, 

 as various geologists believe was the case with some 

 Trilobites. The legs are fitted for crawling about, 

 but, as is frequent in animals living in sea-water, they 

 are also weak and thin. The Serolis is a slow 

 crawler and swimmer, and is usually found on sea. 

 weed. Some geologists have imagined that a few 



Trilobites had genetic relations with the common 

 Apiis of our ditches and ponds. Sufficient has been 

 said, however, to show how large a middle space 

 the numerous family of Trilobites occupy. At the 

 one extreme they nearly touch the King-crabs, and 

 at the other the aborted shrimp-parasites, as in the 

 case of Agnostiis. Perhaps the living Serolis better 

 rejiresents the average forms of Trilobites than any- 

 thing else. 



Fig. 56. Serolis Falricii. Fig. 57. Underside o'i Scrolls Fahricit. 

 a. Eyes. b. Feet. c. Organs of Mouth. 



Fig. 58. A/>!is Jiroduciiis. 



The Cambrian strata have recently been made to 

 extend upwards as high as the " May Hill "group, so 

 as to include rocks formerly classed as Lower 

 Silurian. They are well represented in many parts 

 of Great Britain, notably in North Wales and the 

 Lake districts. Trilobites of various genera may be 

 met with in many localities which are usually visited 

 by tourists for the sake of the scenery alone. It is 

 one of the privileges of the geologist, that his calling 

 takes him tosome of the wildest, grandest, or most beau- 



