92 PROCEEDINGS OP THE ACADEMY OF 



description of that species given by Green and Hall, seems to show 

 that our fossil cannot be properly considered identical. In the 

 first place, it differs in having the mesial lobe only just half as 

 wide as each of the lateral (measuring both at their anterior 

 ends), instead of only about one-third as wide (see dimensions 

 D. myrmecophorus, given in the Fifteenth Report, Regents Univ. 

 N. Y., on State Cab. N. H., p. 18). Again, it shows no traces 

 whatever of nodes or spines (excepting the marginal spines) on 

 any of the segments, either of the mesial or latex'al lobes ; while 

 in Green's species the segments of the lateral lobes are described, 

 in the Regents' Report above cited, and also by Green, as being 

 marked by one or two rows of nodes, and those of the mesial 

 lobe are described in the Regents' Report as being marked each 

 by three spines. Our species also shows a faintly impressed mesial 

 line along each segment of the lateral lobes, not mentioned either 

 by Hall or Green in describing D. myrmecophorus. 



Green gives the number of segments in the middle lobe of the 

 pj^gidium as fourteen, and in each lateral lobe as thirteen; while 

 in apparently a larger specimen (three inches in length). Prof. 

 Hall counted twenty-four segments in the axis, and twenty in 

 each lateral lobe ; from which we may infer that the number of 

 segments varied somewhat with the size of the specimen in that 

 species. 



Although nothing is known of the cephalic shield of this species, 

 or, I believe, of that described by Green, I have little or no hesi- 

 tation in expressing the opinion that at least the form here under 

 consideration possessed the peculiar perforated or digitated exten- 

 sion of its anterior margin seen in D. selinurus, and hence that 

 it belongs to Mr. Conrad's subgenus Odontocephalus. 



Another specimen in the collection from the same locality and 

 position as that from which the foregoing description was made 

 out, consisting of a rude cast of the p^^gidium, shows the same pro- 

 portional breadth of the mesial and lateral lobes, and apparently 

 about the same number of segments, but differs in being propor- 

 tionally longer, its length being to its breadth as about 8 to 11, 

 instead of about 8 to 13. It also differs in having the spines on 

 each side of the truncated posterior extremity distinctly larger 

 than in the form above described, and directed straight backward 

 as in D. selinur-us, instead of converging, as in the last. The 

 spines along its lateral margins, however, are, on the contrary, 



[July 4, 



