26 Remarks on the Trilohite. 



V 



the earliest example of an articulated animal found among the 

 ancient inhabitants of our globe; and although in some few existing 

 genera we find certain points of analogy in their organization, the 

 whole race probably became extinct after the subsidence of the 

 great coal formation. Dr. Backlaad remarks, "No trilobites have 

 yet been found in any strata more recent than the carboniferous 

 series; and no other crusiaceans, except three forms which are 

 also entomostracous, have been noticed in strata coeval with any 

 of those that contain the remains of trilobites ; so that during the 

 long periods that intervened between the deposition of the earliest 

 fossilliferous strata and the termination of the coal formation, the 

 trilobites appear to have been the chief representatives of a class 

 which was largely multiplied into other orders and famihes after 

 these earliest forms became extinct." 



From the multitude of trilobites and fragments of trilobites 

 which have been discovered in different parts of the world, most 

 of which present nothing but portions of the upper shell of the 

 fossil, the discovery of the figure of the under side of the animal, 

 and of the form and arrangement of the organs of locomotion, 

 seems almost hopeless. As the solid parts of the animal struc- 

 ture alone are for the most part susceptible of petrifaction, it is 

 not to be expected the softer portions would leave any traces 

 whatever in the rocks which have entombed and so perfectly 

 preserved these ancient inhabitants of our planet ; for these rea- 

 sons, and some others which we shall presently mention, the legs 

 of the trilobite have been supposed to be soft and very perishable 

 paddles. 



Although much controversy formerly existed as to the true na- 

 ture of the trilobite, it is now admitted by all naturalists to occupy 

 a place among crustaceous animals. The existing genera to 

 which they are most analogous in their general structure are the 

 serolis, the limulus, and the branchipus. In our monograph we 

 announced the discovery of a recent trilobite in the southern 

 seas, near the Falkland islands: this proves to be a species of the 

 genus serolis established by Dr. Leach. In the configuration of 

 its upper shell it approaches exceedingly near to that of some of 

 the trilobites ; the chief difference between the recent and fossil 

 animal consists in the crustaceous legs and antennae of the serolis. 

 The analogies existing between the limulus and our fossil, as we 

 mentioned in another place, have been shown by Dr. Dekay and 



others. 



