FROM THE CARBONIFEROUS FORMATION. 155 



some of the segments there appears to be a feeble wrinkling or faint corrugation of the sur- 

 face. In general only the bases of the spines are present, which so far as can be deter- 

 mined show a disposition very similar to what is seen in the other specimens, but exhibit 

 more clearly than they the relation of the subdorsal series to each other as to distance, 

 showing that they are almost as far removed from each other as they each are from the 

 pleurodorsal series ; one or two spines also of this latter series remain and by their structure 

 show that they probably did not differ at all from those of the other series, unless possibly 

 they were slighter and shorter. 



The legs do not appear, but on the ventral plates their insertion is plainly visible (PI. 

 11, figs. 2-3), showing that the basal joints were probably obliquely appressed, for the coxal 

 cavities are obovate and directed toward the anterior outer edge of the ventral plate next 

 in advance of that on which they are seated ; they are also seated a little posteriorly upon 

 the ventral plate, for they reach its posterior edge, but are separated from the anterior bor- 

 der by about one third their own shorter diameter ; those of the same ventral plate are also 

 separated from each other by a space equal to at least their own longer diameter. 



In the flattened part showing the ventral plates, these extend just as far laterally as the 

 dorsal plates, and the distance from the outer edge, which is preserved upon one side, to their 

 median line is even greater than to the median line of the dorsal plates, showing certainly 

 that they had a wide extent and covered at least the entire under surface of the body ; 

 they were of equal size throughout, narrowing only at their extreme lateral extension where 

 they appear to have been rounded. Their length is 2.25 mm. Outside the base of each 

 leg and abutting upon it are the large oblong-ovate spiracles (PI. 11, figs. 2-3), running 

 transversely to the body, and showing as a deep groove with a very thin laminate ridge 

 along the middle ; they are 2.5 mm. long, 0.6 mm. broad. Lying next the front edge of 

 each ventral plate and on either side of the medioventral line of the body, almost attin- 

 gent at their slightly swollen bases, are the branchial cups (PL 11, figs. 2-4), which appear 

 from within as sunken pits, rounded triangular in form, two sides of the triangle being 

 formed by the median line of the body and the front edge of the segment, the latter being 

 the longer; all the angles are well rounded ; the floor of this pit is flat, but depressed 

 around the edges, so that the deepest part forms a groove just at the base of the bounding 

 walls ; the surface of the floor has in some a spongy aspect with an appearance of converg- 

 ing laminae, but this is not clear ; these branchial pits are a third as broad again as long, 

 being: 1 mm. in breadth and about 0.75 mm. in leno;th. When viewed from the cast show- 

 ing these organs as they probably appeared upon the outside of the body (PL 11, fig. 4), 

 they appear as crater-like elevations, the rim of which is suboval rather than triangular, 

 with the posterior inner angle of the boundary wall somewhat higher and thicker than the 

 rest; the floor presents nearly the same aspect as in the other face. 



This specimen was sent to me by Mr. Pike after I had seen and studied the large and 

 perfect specimen last mentioned. In studying that I had become convinced of the possible 

 aquatic life of the creature from the structure of the long paddling legs, and stated my belief 

 at a meeting of the Boston Society of Natural History held October 20th last. It was 

 therefore with no small pleasure that I subsequently found my conclusions supported in so 

 remarkable a manner by the discovery of these structures on a second individual of the 

 species. Another specimen received from Mr. Carr is as small, as that last mentioned and 



