The specimen represented in the accompanying figure was obtained I from the Coal-measures of Westhoughton, near Bolton, Lancashire, and has been kindly lent to me by Mr. Thos. Midgley, of the Chadwiek Museum, Bolton. It is the nearly complete abdomen (opisthosoma) of an arachnid of the order Anthracomarti. The concavity of the outer margins of the pleural laminæ, producing the scalloped outline shown in the figure, indicates at once that the specimen must be assigned to the family Brachypygidæ; but it is less obvious to what genus it may belong. Mr. Pocock's monograph (see preceding footnote) gives only two genera as known in the family, namely Brachypyge, Woodward, and Maiocercus, Pocock. Comparison between these two is rendered difficult by the fact that of the former only the dorsal surface is known, of the latter only the ventral; of neither has any part but the opisthosoma yet been recognized. Accordingly, in differentiating his genus Maiocercus from Brachypyge, Mr. Pocock was compelled to fall back upon two characters—the general shape of the opisthosoma and the angles made by the anterior pleural laminæ. Brachypyge is defined as having the “opisthosoma much longer than wide; pleural laminæ of the second and third pleura-bearing terga inclined slightly backwards” Maiocercus as having the “opisthosoma much wider than long; pleural laminæ of the first, second, third, and fourth sterna inclined slightly forwards”.