FROM THE CARBONIFEROUS FORMATION. 153 



than the other spinules ; of the front and hind spinules, the posterior is generally longer and 

 slenderer than the anterior, and situated higher upon the stalk ; the double set of holes 

 next the base of the legs in several segments of the body indicates that this was the case 

 also with the lateral spines ; these spinules are longer on the posterior part of the body 

 than oh the anterior, and have about the same angle from the main stem as the terminal 

 forks from each other. The spines occur, one to a segment in each row, on every segment 

 behind the head ; on the penultimate and antepenultimate the main spine seems to end 

 where the spinules spring out, and the latter are of unusual length ; on the last segment 

 the same arrangement occurs, though the spinules are very short. The main spines are of 

 uniform size throughout most of their extent, but enlarge slightly above where they fork, 

 and below where the spinules diverge ; the spinules are generally tapering and pointed, but 

 in the front part of the body the anterior and posterior ones are stout, often scarcely taper, 

 and are bluntly tipped. The length of the spines is from 12-13 mm., and they are 1.6 mm. 

 in diameter in the middle. 



The legs 1 (PI. 11, fig. 11) are better preserved than in any other of the Archipolypoda 

 examined ; the creature is crushed in such a way that one sees in a groove, running 

 beneath the dorsal plates for the greater part of the body, the interior surface of the basal 

 joints of the lower lying legs (the remaining portions of which are buried in the matrix), 

 and just below these upon the plane of the dorsal plates, the exterior surface as well as all 

 the rest of the legs of the upper lying or nearer pairs. They consist of six joints. The first 

 is about twice as long as broad on a side view, narrowing a little at either end ; it is about 

 as broad as possible, the series occupying almost the entire space below the segments so as 

 to crowd against each other ; it is apparently a little compressed, the outer surface furnished 

 with a distinct longitudinal carina at both anterior and posterior edge and furnished also 

 with a very prominent and stout median longitudinal carina, which is generally a little 

 curved ; corresponding to which on the inner face is a rather deep and very abrupt sulca- 

 tion. The second joint is very different ; it is laminate, nearly equal, considerably nar- 

 rower than the basal joint, very long, being more than six times as long as broad ; it has 

 a distinct median carina, at least on the outer side, or perhaps the slightly convex sides 

 are pinched or angulate along the middle; in some instances the one, in others the other 

 appears to be the case, even on adjoining legs. The third joint exactly resembles the sec- 

 ond, except in being shorter ; it has about the same width, and the same median carina, but 

 it is only about half as long again as broad, equal, quadrate and laminate. The fourth joint 

 is of the same length as the third, but slenderer, a little tapering and with only slight trace 

 of the median carina. The fifth is as long as the fourth, continues the gentle tapering of 

 the leg so as to be nearly half as broad as the second joint, and has no carina. There is 

 pretty certainly another still slenderer and apparently cylindrical joint of about equal 

 length beyond this, but it is only preserved in one or two instances and in part. Nothing 

 positive can be asserted of the claw, but one leg appears to have a single slender gently 

 curving claw of considerable length. The legs are at first sight apparently shorter at the 

 two ends of the body than in the middle, but this is due simply to imperfect preserva- 



1 Between the tips of two of the legs may be seen a crushed considered by Dr. Dawson (Proc. Bost. Soc. Nat. Hist., 

 molluscan shell, having the appearance of a minute Planorbis, xxi, 157) as Spirorbis (Microconchus) carbonarius. 



MEMOIRS BOST. SOC. NAT. HIST. VOL III. 20 



