64 ARRANGEMENT OF THE GEOPHILIDM—COOE. vol. xviii. 



could be iuferred while the opiniou held that the so-called /'i^ectinate 

 lamellaj" in the two cases were structural equivalents. 



That the dentate lamellte have been sui^pressed in Dicella and Orya 

 is a case of apparent similarity between genera distinct by nearly all 

 possible characters, and an example of the principle that the presence 

 or suppression of a primitive structure or character is not of itself an 

 evidence either of close aftinity or wide divergence. 



Since the publication of Meinert's works the number of described 

 genera has greatly increased ; likewise the desirability of some arrange- 

 ment whereby their affinities may be made apparent. Unfortunately, 

 the descriptions of new forms are often very incomplete and omit the 

 most important data, those to be drawn from the mouth parts. Not- 

 withstanding this neglect, it is evident from many specific descriptions 

 that the number of genera yet to be recognized is considerable, and it 

 would seem that a statement of the affinities already manifested will 

 aid in subsequent study. 



That a complete arrangement, such as is here j)roposed, can in the 

 present state of the subject be entirely correct or satisfactory is not to 1 

 be exi)ected. Cases of uncertain and deficient data are noted in sev- 

 eral places. The groups here proposed as families seem to have, by j 

 analogy with other classes and with other Chilopoda, ample structural 

 basis for such recognition. The external form and habit are almost j 

 identical for the entire group, and the structural differences are not to 1 

 be explained as correlated with adaptations to localities or hosts, but 

 are rather the accumulated result of variation without the interference 

 of any important principle of selection, a history the more possible 

 because the changes are mostly in the direction of degeneration. From 

 this consideration we may explain the confusing fact that in the difl'er- 

 ent groups there are frequent examples of the preservation of some 

 primitive character which the other members of the family may have 

 lost, and on the other hand there are numerous cases of parallel varia- 

 tion. Of this last the pleural pores are a good example. These may 

 be numerous and distinct, doubtless the primitive condition, and the 

 one which appears in Scolopendrida^; they may be clustered about two 

 or more large cavities in the pleurte, or they may be entirely wanting. 

 In the genus Geophihis the first and second conditions are present, and, 

 if some descriptions are to be trusted, also the third. To suppose that 

 a character which may differ in closely related species can be of use as 

 an evidence of affinity between genera or families would be clearly 

 unreasonable. And yet poriferous foveohe entirely similar to those of 

 some species of Geophilus occur in SehendyJa and several related 

 genera, in BaUophilns. and Dignatliodon. Thus animals with widely 

 divergent types of labrum, mandibles, and other parts, live in the same 

 localities, have the same habits, and eat the same food with appar- 

 ently equal success, so that it seems impossible to imagine that special 

 advantages pertain to the different adaptations. 



