OF TRILOBITES. 9 



resemblance. But this resemblance totally fails when we examine the under side of the 

 animal ; for all the researches hitherto made (and they are many) fail to detect the slightest 

 trace of limbs in the Trilobite. It is impossible, seeing the state of preservation in which 

 they occur, to suppose that in every case, — in fine shale, in limestone, in arenaceous mud, — 

 all traces of these organs should have been lost, had they ever existed. 



We are compelled to conclude that Trilobites had not even membranaceous feet, and 

 that the ventral surface was destitute of appendages. It is of course difficult to prove 

 this. And almost all naturalists are disposed to allow them soft gills, attached to the 

 under side. I do not see that the Trilobite had any need of appendages, further than what 

 might be necessary as breathing organs. In this I have the concurrence of Prof. Wyville 

 Thompson, who has given some thought to the affinities of the group. If gills existed at 

 all, they were probably quite minute. 



There is some reason to believe that, like its predecessor, the Annelide, the habit 

 of the Trilobite was to gorge itself with the carbonaceous mud, and extract from it the 

 nutritive portions. Such material has, indeed, been found in the straight intestinal canal 

 of the Trilobite. Barrande has figured a specimen in which this viscus is preserved, a 

 natural cast being taken of the interior by the sabulous matter swallowed by the animal. 1 

 What the nature of this sabulous matter was originally may be matter of conjecture ; but 

 it was solid enough to retain the stomach and intestine in a dilated form, while the sur- 

 rounding matrix was solidified. It must, therefore, have consisted of a hard food, such, 

 for instance, as the shells of Lingulse, or, if the habit was carnivorous, of the contents of 

 the bodies of the worms devoured, — or, lastly, of the silty mud among which the creatures 

 lived. Against the former supposition we have strong reason to conclude, for Trilobites 

 certainly possessed no hard jaws capable of comminuting shells or corallines, which we 

 know existed during the same period. I see no likelihood of the carnivorous habit, and 

 venture the latter suggestion. Mr. Spence Bate also thinks the mouth was contractile. 



The only hard portion of the under side is the immoveable upper lip or labrum ; and 

 this may have been the instrument by which the food was scraped together. The 

 absence of feet, and the presumed nature of the food would give me reason for believing 

 that the Trilobite did not swim, as supposed by many authors, but crawled along the 

 bottom. The shape was fitted for this j all Trilobites, whatever be their ornament on 

 the upper side, present an even contour round the margin, which would apply itself to a 

 flat surface accurately, while the under side was no doubt smooth and soft. 2 Probably, 

 in many cases, the Trilobite lay half-buried in the silt, as is the frequent habit of the large 

 Limulus, or King-crab. 



1 In the genus Trinacleus, vol. i, pi. 30, fig. 38, of the ' Systeme Silurien de Boheme,' par Joachim 

 Barrande, 1852, Prague and Paris, vol. i. A magnificent and costly work, of which only the Trilobites 

 are yet published. 



2 The analogy with Chiton, perceived by some of the old writers, is not altogether fanciful. At least, 

 the habit must have been very similar, though of course there is no direct relation. 



2 



