154 



THE MYRIAPODA OF NORTH AMERICA. 



Fam. IV. SCOLOPENDEID^E, Leach* 



Segruenta podophora 21 — 23. Oouli pauoes vel nulli. Pedes postremi incrassati, plerumque spinosi. 



Feet-bearing segments 21 — 23. Ocelli few or none. Last pair of feet thickened and generally spinous. 



In this family the principal generic characters are founded upon the number of the seg- 

 ments of the body, the shape of the head, the number and form of the spiracles, the 

 absence or presence of eyes, and the form of the terminal segment and its appendages. 

 In some cases the number of joints of the antennae seems to be a constant generic sub- 

 character. In the large genus Scolopcndra — the Titans of the Myriapoda — the principal 

 specific characters are founded upon, first, the number of segments to the antenna; ; 

 secondly, the number and arrangement of the labial teeth ; thirdly, the peculiarities of the 

 posterior feet ; fourthly, the shape and comparative size of the head. I have no doubt 

 that the number of joints to the antenna? is fixed for most species, but it serves more 

 generally to distinguish groups than single species ; yet it occasionally is the most reliable 

 character separating closely allied forms. Unfortunately it must be used with great cau- 

 tion in the identification of individuals ; for, owing to the ease with which portions of the 

 antenna; are lost, the want of a certain number is a very indefinite negative character. 

 After detaching a few of the; distal joints, no trace of their former presence is left. For 

 the same reason much caution is also necessary in assigning the number in a description. 

 M. Saussure has found so much variation in this character that he considers it worthless. 

 It is possible that it may vary in certain species ; but the differences generally consist in 

 there being too few joints, which, as has been just stated, is to be looked for, and repro- 

 duced antennee probably have occasionally an abnormally great number of very small 

 articles. The number and arrangement of the labial teeth sometimes constitute a good 

 character, but there is often an agreement between distinct forms, and on examining large 

 suites of individuals, I have found more variance in the same species than reading would 

 lead one to look for. The posterior legs furnish the best criteria in the distinguishing of 

 species. Most species have peculiarities either in the shape or relative size of the joints, 

 or in the number or arrangement of spines on them. In order to show the amount of 

 constancy that these characters possess, I have drawn up a series of tables, which may aid in 

 establishing their value. The color, I think, is not to be depended upon, although Mr. 

 Newport seems to attach much importance to it. In the preservation of specimens it is 

 very liable to be altered or destroyed ; besides this fact, my studies of these animals, both 

 in museums and, to a limited extent, in the Tropics, lead me to the opinion that the color 



* Linn. Trans, xi. 



