FROM THE CARBONIFEROUS FORMATION. 



151 



Acantherpesles major. 



one of which is very pei'fect and of enormous size, and which was first shown me by Prof. 

 J. W. Pike ; the other though only fragmentary is the more interesting because it exhibits 

 the ventral plates more clearly than any other specimen of Archipolypoda yet discovered. 

 A third specimen with its reverse, representing a younger individual, has more recently 

 been placed in my hands by Mr. Pike. 



In the specimen figured in the Illinois Eeport, and which by the kindness of Professor 

 Worthen we are able to reproduce here, we have a lateral view, apparently of the ante- 

 rior part of the cylindrical body a little curved downward, in which the scars of the lower 

 Spines and the mammiform bases of the other 

 series are present, besides one or two of those 

 of tbe uppermost row upon the further side of the 

 body. The width of the body shows how huge the 

 creature must have been. Judging by compar- 

 ison with the most complete one I have seen, it 

 must have been three decimeters or just about 

 one foot long ; " it probably attained a length of 

 12 to 15 inches " say the describers. The seg- 

 ments, which are about three times as broad as 

 long, are divided transversely into two parts, the 

 arched anterior portion a little longer than the flat posterior part and bearing the spines. 

 The surface is apparently smooth. The spines are altogether wanting beyond their bases 

 with the exception of a single fragment in the uppermost row ; and this is evidently one 

 of the basal spinules and not the spine itself, being comparatively small, simple and conical. 

 The bosses and scars, however, show that there was a subdorsal row of spines tolerably near 

 the mediodorsal line, another at the lower portion of the dorsal plate and a third pleuro- 

 dorsal row considerably nearer the former than the latter. The legs are mostly broken off" 

 near their bases, but two or three are longer, and one is represented in the figure (not men- 

 tioned in the text) as complete, being regularly conical, shorter than the body, and divided 

 into five nearly equal joints ; I cannot doubt that this and the apparent joints of the other 

 legs are either given quite inaccurately or that at all events the marks do not represent 

 the joints of the legs. The length of the fragment is 62 mm. and its width 21 mm. 



The most complete specimen seen (PI. 11, figs. 6-8, 11), exhibits a side view of appai'ently 

 the entire creature, the greater part of the body in a straight line, but the anterior part curved 

 a little upward ; along the entire upper line the spines of the subdorsal series may be seen, 

 many of them very perfect ; the position of the other rows may be traced by the pits 

 in the body itself, while legs, many of them almost pei'fect, may be traced along nearly 

 the entire lower margin. The body is cylindrical or nearly cylindrical in form, perhaps a 

 little higher than broad, tapering forward from the seventh or eighth segment so as to 

 be from one fifth to one fourth smaller ; and backward from the twelfth or thirteenth seg- 

 ment very uniformly and gradually, so as to be at tip only about one half the greatest 

 breadth. The whole length of the body is 207 mm., its greatest breadth 16 mm. There 

 can hardly be any doubt that the whole animal is preserved. The rapidly tapering form 

 of the extreme hinder extremity with the change in the characteristics of the spines make 

 it certain that the body ended here ; at the front extremity the first segment has every 



