174 NATURAL SCIENCE. Sept.. 



Mr. Beeby Thompson, in the last number of the Quarterly 

 journal of the Geological Society (August, 1894), ^^^ examined all 

 previous writings on the subject, investigated the matter, and 

 concludes that the peculiar characteristics are due to interbedded 

 layers of vegetable matter, which continued to decompose and evolve 

 carbonic acid gas and marsh gas after deposition ; and that 

 where a layer of extra thickness occurred, the decomposition con- 

 tinued whilst a thickness of several inches of new sediment was laid 

 down, with the result that arborescent markings were produced along 

 the lines taken by the escaping bubbles. Mr. Thompson, in this 

 interesting paper, gives his reasons for these conclusions, and records 

 his experiments to reproduce artificially the characteristics of 

 landscape marble. 



The Systematic Position of Trilobites. 



For many years the position of the Trilobites in the scale of 

 organised beings has been doubtful. One school has insisted that 

 they should be referred to the Crustacea, and another to the Arach- 

 nida. Mr. H. M. Bernard has just published, in the Quarterly Journal 

 of the Geological Society (Aug., 1894), ^^ important zoological paper in 

 which he discusses at length the question, and refers these ancient 

 life-forms definitely to the Crustacea, the original position assigned 

 to them by Linnaeus and by Burmeister. We are unable to give 

 the details of Bernard's paper, but quote his own words as given in 

 his " summary " : — 



" It is now possible .... to fix with great probability the 

 zoological position of the Trilobites. The bending round ventrally 

 of the first segment, the great labrum with antennae attached at its 

 sides, the ' wandering ' of the eyes, the pores (pointing to the probable 

 presence of water-sacs), the head with a varying and progressively 

 increasing number of segments, the dorsal organ, the rudimentary 

 character of the posterior segments, and the gradual diminution in 

 size, with the essentially lobate or phyllopodan type of the limbs, all 

 serve to connect the Trilobites with Apus. 



"This relationship cannot, however, be considered as direct. Apus, 

 on account of its richer segmentation, the absence of pleurae on the 

 trunk-segments, and its more membranous parapodia-like limbs, 

 must be assumed to lie in the direct line upwards from the original 

 annelidan ancestor towards the modern Crustacea. The Trilobites 

 then must have branched off laterally from this line either once or 

 more than once, in times anterior to the primitive Apus, as forms 

 specialised for creeping under the protection of a hard imbricated 

 carapace. This carapace was obtained by the repetition, on the 

 trunk-segments, of the head-shield which, as we have already seen, 

 almost certainly existed as a structure sui generis in earlier forms, 

 and, someAvhat modified, has been retained as such in the early 

 -Crustacea proper (' Aspidophora '). 



" It seems to me, therefore, that the Trilobites, studied in the 

 light of new discoveries, especially of those which we owe to American 

 investigators, yield the most interesting and important evidence as to 



