Geological Society of London. 231 



The author, in his work on " The Apodidse," endeavoured to 

 show that the Apus was the ancestral form of all existing Crustacea 

 except the Ostracoda, and as such might be expected to throw light 

 upon the Trilobites. Since the publication of this work he has 

 been studying the organization of the trilobites themselves, and the 

 results are given in the present communication. He discusses the 

 great variability in the number of segments shown by the trilobites ; 

 the formation of the head by the gradual incorporation of trunk- 

 segments ; the bending round ventrally of the first segment; the 

 " wandering " of the eyes; the existence and modification of the 

 "dorsal organ; " and especially the character of the limbs. 



As a result of this discussion, he states that the zoological position 

 of the trilobites can now be fixed with considerable probability. 

 The features described serve to connect the trilobites with Apus. 

 Apus must be assumed to lie low in the direct line up from the 

 original annelidan ancestor towards the modern Crustacea, and the 

 trilobites must have branched off laterally from this line, either 

 once or more than once, in times anterior to the primitive Apus, 

 as forms specialized for creeping under the protection of a hard 

 imbricated carapace, obtained by the repetition on every segment of 

 the pleuree of the head-segments, which together form the head- 

 shield. 



The trilobites may be briefly described as fixed specialized stages 

 in the evolution of the Crustacea from an annelidan ancestor with 

 its mouth bent round ventrally, so as to use its parapodia as jaws. 



2. "Landscape Marble." By Beeby Thompson, Esq., F.Gr.S., 

 F.C.S. 



The Gotham Stone is a hard, close-gi'ained, argillaceous limestone 

 with conchoidal fracture. The dark arborescent markings of the 

 stone rise from a more or less stratified dark base, spi'ead out as 

 they rise, and terminate upwards in wavy banded portions of the 

 limestones. In some specimens two " landscapes " are seen, one 

 above the other, each rising from a distinct dark layer. 



The author describes the microscopical and chemical characters 

 of the rock, and its mode of occurrence, and discusses the explana- 

 tions which have been put forward to account for its formation, 

 especially that of Edward Owen, who in 1754 gave the first pub- 

 lished description of the Gotham Stone, and that advanced by Mr. 

 H. B. Woodward in the Geological Magazine for 1892. He then 

 proposes a new explanation to account for the formation of the rock, 

 and maintains that its peculiar characters are due to interbedded. 

 layers of vegetable matter, which decomposed and evolved carbonic- 

 acid gas and marsh-gas. This decomposition continued while several 

 inches of new sediment were laid down, the result being that arbor- 

 escent markings were produced along the lines taken by the escaping 

 bubbles, and that the upward pressure of these gases, after their 

 escape had been prevented by increasing coherence or greater 

 thickness of the upper layers of sediment, caused the corrugations 

 in the upper surface of the stone. He further discusses the com- 

 position of the stone, and describes experiments which he made to 

 illustrate his views. 



