FROM THE CARBONIFEROUS FORMATION. 169 



body are distant from each other, and probably quite as near the lateral rows as they are 

 to each other ; the spines of the subdorsal ro v ws, which only are preserved in their entirety, 

 are less than half as long as the breadth of the body, stout, conical, curving backward, 

 finely pointed, and bear near the middle a delicate anterior spinule. The legs are repre- 

 sented as tolerably stout, a little longer than' the width of the segments and composed of 

 five equal joints. 



The first of the specimens I have seen which I refer to this species, and in which we have 

 both obverse and reverse (PI. 12, figs. 22, 25, 26), was received from Mr. Worthen, and 

 shows a partly dorsal partly lateral view of most of the body, the head end missing, curving 

 upward near the middle so as to be bent nearly at right angles. The anterior half of the 

 fragment is uniform in width ; behind, it tapers slightly and regularly, so that the poste- 

 rior end is about two thirds as broad as the stoutest portion. The entire length of the 

 fragment is 60 mm. and its greatest width 4.25 mm. There are twenty-seven segments 

 preserved, varying from 2 mm. to 2.5 mm. in length, i.e. they are about twice as broad as 

 long, or somewhat broader than that ; transversely they are not very strongly arched, 

 indicating a somewhat flattened body ; longitudinally they are very strongly divided into 

 two parts, the anterior two-thirds being very much elevated, ridged and spiniferous, the 

 posterior third deeply sunken ; between the subdorsal spines is a slight, dull, transverse 

 furrow. Over all the segments may be noticed distinct, close granulations, a little coarser 

 on the lower non-spin iferous parts of the segments, and more apparent in the front than in 

 the hinder portions of the body ; they appear in the cast of the upper surface and therefore 

 indicate, as Meek and Worthen say, a pitting of the exterior crust (PL 12, fig. 24). 



The spines of the lateral rows are far down the sides of the body, while the subdorsal rows 

 approach them, being set very widely apart ; those only of the lateral rows are preserved 

 (PL 12, fig. 24), and are rather more than half as long as the width of the body, tolerably 

 stout, tapering, curved slightly backward, and not very sharply pointed; they have a 

 slight anterior spinule springing from the extreme base. The legs are present along the 

 whole under surface, which is so preserved as to show well the basal joints ; these are not 

 so stout, comparatively speaking, as in Acantherpestes major, and taper a little, the adjoin- 

 ing legs not touching each other at base but separated by a considerable space ; the basal 

 joint is evidently compressed, subquadrate, with a not very pronounced median carina, 

 terminating squarely, a little longer than the basal breadth, and about 1.1 mm. long; tile 

 second joint is long and slender, nearly as broad as the tip of the first and about six times 

 as long as broad ; it is laminate, straight and equal, with a median carina of no very great 

 prominence ; its length is about 2 mm. and its breadth 0.32 mm ; a third joint is some- 

 times visible and is slightly narrower, and only a little longer than broad, quadrate, appear- 

 ing as a mere continuation of the second ; all the parts beyond are broken off in all the 

 legs, the longest of which is 4 mm. where the body is of the same width. 



A second specimen belonging to the collection of Mr. Carr (PL 13, fig. 13) exhibits on 

 one stone the entire length of the animal, and on the counterpart almost the whole. It lies 

 in a nearly straight line upon its side, showing the spines on one side and the legs on the 

 other, somewhat faintly and imperfectly, but throughout nearly the entire extent of the body. 

 There are nearly forty segments besides the head, but the exact -number cannot be deter- 

 mined from the obscurity of some parts. The length as preserved is 63.5 mm. which, if 



MEMOIRS BOST. SOC. NAT. HIST. VOL. III. 22 



