406 R. I. Pocock — The Carboniferous Arachnid Anthracosiro. 



The other specimen, No. 1556, is the more important and 

 instructive of the two. It is the fossil of a much smaller animal. 

 One half of the nodule of clay-ironstone in which it is imbedded 

 shows the dorsal surface ; the other the impression of the latter.^ 

 The chief feature of interest is the excellent state of preservation of 

 the carapace. In the type of A. woodwardi this plate is crushed, 

 showing nothing but the shape of its outline. Concerning its 

 probable structure, I remarked that its crushed condition suggests 

 that its median area was axially elevated, as in EopJiryniis prestvicii 

 and Kreischeria wiedei, and that it was justifiable to conclude that 

 it was constructed essentially as in these genera. The fossil under 

 notice proves the first suggestion to be true ; the second false. The 

 carapace is strongly arched, both longitudinally and transversely. 

 From its highest point, which lies in advance of the middle, it slopes 

 downwards, both anteriorly and laterally, and a pair of obtuse 

 ridges, diverging somewhat abruptly from the middle line, then 

 curving inwards and downwards, extends backwards almost to the 

 posterior border of the carapace. The area between these ridges is 

 widely and somewhat deeply excavated ; externally to them the 

 surface slopes downwards to the lateral margin. Anteriorly each 

 ridge forms a smaller curve, also with its convexity outwards ; and 

 nearly midway between this and the lateral border there is a very 

 distinct ocular tubercle. The outline of the carapace is almost 

 exactly the same as that figured for A. woodioardi. There was 

 possibly a small median process projecting forwards from the 

 anterior border, and the posterior portion presents a short horizontal 

 area as in the last-named form. 



Anthracosiro fritsehii, s-p.-Q., dorsal swciacQ. X 7|. 



The tergal plates of the opisthosoma agree in the main with those 

 of A. woodwardi, with the exception that the first is relatively 

 much shorter. It appears upon the impression as a short sclerite, 

 not half the length of the succeeding plate ; but upon the fossil 

 itself it is invisible, so that the opisthosoma appears to be supplied 

 with but seven tergal plates on the upper side. The median line 



