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E. Leonard Gill — A Carboniferous Arachnid 



those attributed to Maiocercus, the other criterion, the proportion of 

 length to breadth, does not help us, since the length and breadth are 

 as nearly as possible equal. Nevertheless I am disposed on general 

 grounds to refer this specimen, with very little hesitation, to Matocercus. 

 If I am justified in doing so, the specimen not only necessitates 

 a slight modification in the definition of the genus, but adds largely to 

 our knowledge of it. It is the dorsal surface that is shown, and up 

 to the present only the ventral surface of Maiocercus has been described. 

 Since the dorsal surface of the opisthosoma of Brachypyge is well 

 known (from Dr. Woodward's figure, copied in Mr. Pocock's mono- 

 graph), direct comparison is possible between it and the present 

 specimen. Considerable differences are obvious. The most important 

 are those relating to the axial parts of the tergal plates, which are 

 proportionately much wider than in Brachypyge ; whilst the eighth 

 tergum is not fused, as in Brachypyge, with the inner parts of its 



Fig-. 1. Maiocercus orbicularis, sp. 

 nov. Coal-measures, West- 

 houghton, near Bolton (dorsal 

 surface of opisthosoma) . 



FIG. 2. Maiocercus orbicularis, sp. 

 nov. (restored outline of opistho- 

 soma). — Both figures drawn three 

 times nat. size. 



pleural laminae. The various systems of sutures separating and sub- 

 dividing the laminae correspond in a general way in the two forms, but 

 in Brachypyge they are apparently much more strongly marked than 

 in this specimen from Westhoughton. A. similar direct comparison with 

 Maiocercus, of which only the ventral aspect is known, is naturally out 

 of the question, and all that can be said is that the Westhoughton 

 specimen presents us with a dorsal surface which is much what we 

 should expect to find on the back of a Maiocercus. Incidentally it 

 seems to confirm Mr. Pocock's surmise 1 that Maiocercus is in some 

 respects more nearly related to Anthracomartus than to Brachypyge. 



A few points of detail call for mention. The first somite is missing ; 

 the dotted outline in Pig. 2 is intended to indicate its absence rather 

 than its probable form. The ill-defined plate lying in front of the 



1 ' ' Terrestrial Carboniferous Arachnida of Great Britain 

 Society, vol. lxiv, p. 60. 



: Palaeontographical 



