into two separate segments, the posterior of which gives origin to the immense foot-jaws, whilst in the Chilognatha the head is composed of but a single segment. An apparent contradiction of this exists, however, in the Cermatiidæ. When viewed from above, the head of one of this family appears to consist of but a single segment; but this is merely because the two cephalic scuta are fused together and consolidated into one, just as two body scuta are. The sternum of the posterior segment is entirely separate, and bears the foot-jaws as in the other families. In like manner, in the Lithobiidæ, the second cephalic scutum is very small, agreeing with the smaller scuta of the body.
The arrangement of the Chilopoda adopted in this memoir is very nearly that of Mr. Newport, which appears to be the true exposition of the plan of their creation. His families are natural, and are grouped according to their affinities. The Cermatiidæ deservedly stand at the top, on account of their more perfect organization and approach in some characters towards the Hexapoda. They have, as has been just stated, but a single scutum to two segments. In the Lithobiidæ the posterior scuta of each pair is atrophied, evincing a tendency to disappear, and, at the same time, the antennae are almost multiarticulate. It is evident how these two facts ally them to the Cermatiidæ, and indicate a position at the top of the Holotarsia, which is confirmed by the fewness of the segments of the body and their active habits. On the other hand, the tendency of the first subsegments to become enlarged and approach the Diplopod type in the Geophilidæ, indicate their position as low in the scale, which is also confirmed by the great number of the segments of the body and the poorly developed nervous system.
Dr. Leach (Linn. Trans., xi), M. Gervais (Apteres, vol. iv), and Mr. J. E. Gray (Enycl. Anat. Phys., art. Myriap.), have placed the Chilopoda below the Chilognatha, a position which is totally repudiated by their more highly developed nervous and vascular systems, as well as by their habits and external form. They are the carnivora of the Myriapoda, and undoubtedly are superior to the vegetable feeders.
There have been offered, within a few years, three different classifications of the Chilognatha, by Messrs. Newport, J. E. Gray, and J. F. Brandt. Mr. Lucas has also published a synopsis (Hist. Nat. des Crustac. des Arachn. et des Myriap., tome iv, 1840), to which I have not had access, but, according to Mr. Newport, it differs from that of M. Gervais only in the names of the families.
J. E. Gray (loc. cit.) proposes to divide the Chilognatha into six families, the Iulidæ, Craspedesomidæ:, Polydesmidæ, Glomeridæ, Zephronidæ, and Polyxenidæ. He does not attempt to arrange these into higher groups, and totally ignores the existence of the Sugentia! His Craspedesomidæ is probably the same family as that known in this paper as the Lysiopetalidæ, and the others appear to correspond with those of the same names, although his characters are very different.
