FROM THE CARBONIFEROUS FORMATION. 147 



presence in arthropods x ; branchiae also occurring in not a few instances nearer the medio- 

 ventral line of the body than the legs, and branchiae and spiracles coexisting even in the 

 true insects, and then in somewhat similar relative positions (though the branchiae in 

 these instances have never been found next the medioventral line) ; and the presence 

 further of swimming legs leading us to presume in these creatures an aquatic or amphibi- 

 ous mode of life : I believe we may fairly conceive these cup-shaped organs to be bran- 

 chial supports, and that we are dealing here with a type of myriapods very different from 

 any existing forms, — suited to an amphibious life, capable of moving and of breathing both 

 on land and in water. Moreover the assemblage of forms discovered in these Mazon Creek 

 beds lends force to this proposition ; for the prevalence of aquatic Crustacea, of fishes and 

 ferns indicates, what the presence of marsh-frequenting flying insects does not contradict, 

 that the fauna and flora was that of a region abounding in low and boggy land and pools. 



These however are not the only points in which the ancient forms differed from the 

 recent. The modern forms are of uniform size throughout, while the ancient, at least 

 when seen from above, tapered noticeably toward either end and especially toward the 

 tail, the largest part of the body being in the neighborhood of the seventh to the tenth 

 body segments, which were often two or even three times broader than the hinder 

 extremity, and considerably broader than the head or the first segment behind it. A 

 single segment seems to have carried all the appendages related to the mouth parts, 

 while in modern types two segments are required for this purpose. This is inferred 

 solely but sufficiently from the fact, even more remarkable, that every segment of the 

 body (as represented by the dorsal plates), even those immediately following the head, is 

 furnished with two ventral plates and bears two pairs of legs. As is well known, the 

 segments immediately following the head-segments in modern Diplopoda have each only 

 one ventral plate and bear only a single pair of legs, — a fact correllated with the embry- 

 onic growth of these creatures, since these legs and these only are developed at about the 

 time of hatching. The mature forms of recent Diplopoda therefore here resemble their 

 own young more than do these carboniferous myriapods, a fact which is certainly at vari- 

 ance with the general accord between ancient types and the embryonic condition of their 

 modern representatives, and one for which I can offer no explanatory suggestion worth 

 consideration. 



These remarkable points, in which the structure of the carboniferous myriapods are found 

 to be distinguished from modern Diplopoda, none of which (with the single exception of 

 the least important, structurally considered, viz. the spined appendages) have before been 

 pointed out, seem to warrant our placing them in a group apart from either of the modern 

 suborders of myriapods, and of a taxonomic value equivalent to them. For this group, 

 the name Archipolypoda is proposed. 



Unfortunately the preservation of the appendages of the head in these ancient types 

 has not proved sufficiently good to allow much comparison between them and modern types. 

 This is the more to be regretted since these parts are those on which we depend largely 

 for our judgment of the relationship of the Myriapoda to other Insecta and to Crustacea. 

 If they were present and clearly defined we may well suppose that they would afford some 

 clew to the genetic connection of these great groups. 



1 Attention should be drawn in this place to Ryder's recent ially of its tracheal system (Amer. Nat., xrv, 375), the exter- 

 observations on the anatomy of Scolopendrella, and espec- nal openings of which are "inside the bases of the logs." 



