1878.3 299 [Scudder. 



describe under the name of D. Neptuni. These specimens, though 

 gigantic beside Rhachura, show the same general features; the pro- 

 portion of the different segments of the abdomen are almost identi- 

 cal; the lateral caudal appendages are essentially alike, although a 

 median spine is added; the lines of ornamentation are of the same 

 nature and have an equal distribution; they are in many cases 

 branched; on the antepenultimate segment the anterior lines are 

 transverse and with those of the opposite sides form curves, convex 

 in front, while the posterior lines are longitudinal, just as in Rhachura; 

 the general trend of all the lines on the penultimate segment is also 

 the same, this segment differing in this respect from the antepenulti- 

 mate to just the degree we find in the Illinois fossil. The much 

 more numerous lines, however, do not, as in Rhachura, originate from 

 the anterior outer angle of each segment, but from its whole outer 

 margin, the greater part of them parallel to one another; but a curi- 

 ous resemblance to Rhachura again appears in the slight interdigita* 

 tion of the lines of the opposite sides, which, as in Rhachura, appear 

 at first glance to be continuous across the segment. These intimate 

 resemblances show that the two animals were closely allied, but 

 leave it no less surprising that mere marks of ornamentation should 

 in so close a manner happen to resemble the neuration of an insect's 

 wing. Owing to this resemblance it may bear the name of Rhachura 

 venosa. 



Having thus settled the affinities of this fragment, it seems proba- 

 ble that the impression of a dorsal shield in the same nodule belongs 

 to the same individual. This would show that it possessed a cara- 

 pace resembling that of Dithyrocaris in general form. It was, how- 

 ever, very broadly rounded in front, and its periphery had a broad, 

 flat margin, which was covered, at least laterally, with very frequent, 

 delicate but distinct, slightly incurved, uniform ridges, nearly par- 

 allel to the longitudinal axis of the body, and to one another. The 

 specimen is too broken to show anything of the eyes or of any other 

 feature excepting two low longitudinal ridges marked by a slight 

 sharp carina, slightly curved, opening inward, one in the middle of 

 either lateral half of the body. 



Breadth of the carapace 50 mm.; breadth of its margin. 5.5 mm.; 

 greatest distance of lateral ridge from inner edge of margin — on 

 one side, 10 mm.; on the other 8.5 mm. Length of abdominal frag- 

 ment and appendages 48 mm.; of antepenultimate segment 7 mm.; 

 breadth of same 9.5 mm.; length of penultimate segment 13 mm.; 



