512 AN ARACHNID FROM THE COAL 



to it fourteen genera with twenty-four species, grouped in four 

 families. The special interest of the example from Crawcrook, 

 apart from its being a type of fossil hitherto unknown from 

 our coal field, lies in the fact that it is very probably a 

 representative of one of the least known and most recently 

 described genera of Anthracomarti — the genus Anthracosiro, 

 founded by Pocock*' in 1903. A further point of interest is 

 that this specimen seems to show the ventral surface ; not only 

 in the previously known examples of the genus in question, 

 but in nearly all the Anthracomarti that have been found, it is 

 the dorsal side that is shown. 



The fossil exhibits a cephalothorax, an abdomen, and parts 

 of certain appendages. The cephalothorax is in a rather 

 rough state of preservation. The abdomen on the other hand 

 is well preserved. The appendages, in so far as they are 

 represented at all, were originally almost entirely buried in the 

 matrix of the nodule, and it has not been possible to expose 

 them by any means perfectly or completely. The total length 

 of the body is 20 mm. (cephalothorax 6*5, abdomen i3'5)j the 

 greatest width of the cephalothorax as here exposed is 6"5 mm., 

 and of the abdomen 8-5 mm. ; but the full width of the abdomen 

 was probably 11 or 12 mm. 



I have been in some doubt as to the precise aspect shown 

 by the fossil. I am inclined to think, however, that the nodule 

 has split in such a way as to expose for the most part the 

 inner side of the ventral integument. If this be the true reading 

 of it, we look upon it from the dorsal aspect, but see details 

 belonging chiefly to the ventral. A good many Anthracomartid 

 fossils have been described from time to time as showing the 

 ventral side, and in most cases it has proved eventually that 

 they have been so described in error, the mistake having arisen 

 through certain structures of the under-side appearing as im- 

 prints through the dorsal plates. It will be well, therefore, to 

 state the grounds upon which I conclude that the parts here 

 exposed are really those of the under surface. These grounds 



* Bi. I. Pooock, A New Carboniferons Arachnid, G-eol. Mag-., 1903, p. 247. 



