98 PROCEEDINGS OF THE NATIONAL, MUSEUM vol.84 



peds, the various groups of mountains that are scattered through the 

 southwestern deserts afford phenomena of insular restriction, like 

 groups of islands separated by the sea. 



In the family Lysiopetalidae a notable contrast is presented in 

 the distribution of the species, between the Southeastern and South- 

 western States. In the humid region to the east of the Mississippi 

 River the family is represented by a single species, commonly Imown 

 as LysiopetaluTTi lactarium^ though now referred to the genus Spiro- 

 strephon. In the arid Southwestern States the same family group 

 is represented by numerous local species, and among them are found 

 remarkable structural differences that require generic recognition. 

 Though collections have been made in widely separated districts^ 

 the results presented in this paper no doubt will prove to be only 

 a beginning in the work of discriminating the local forms of this 

 specialized group in the Southwest. 



The Lysiopetalidae are among the more hardy and active mem- 

 bers of the milliped group, often living among rocks in rather dry, 

 exposed places, but in situations where it is possible to take refuge 

 underground in the dry seasons. When the animals are disturbed 

 their movements are rather quick, and if touched or injured they 

 emit a defensive "repugnatorial" secretion as a whitish fluid form- 

 ing a line of small beadlike drops along each side of the body. This 

 milky secretion has a very strong and disagreeable odor, entirely 

 different from that of the repugnatorial fluids in other groups of 

 millipeds. 



GENERAL CHARACTERS OF THE FAMILY 



The Lysiopetalidae are associated with two groups of millipeds 

 in the order Coelocheta, which is characterized by numerous body 

 segments, 30 and upward; normally developed mouth parts; slender 

 flexible antennae; well-developed eyes, except in subterranean or 

 cave species; gnathochilarium with large stipes and a triangular 

 mentum behind well-developed lingual laminae; a distinct median 

 suture on all the body segments; absence of pleural sutures or dis- 

 tinct pleurae; free pedigerous laminae; last segment terminated by 

 a pair of slender papilliform setigerous spinnerets; legs long and 

 slender, the first two j)airs 6-jointcd, the others 7-jointed, in a few 

 cases 8-jointed; segment 3 legless; genital openings of males in large 

 apertures of the basal joint of the second pair of legs; copulatory 

 organs replacing both pairs of legs of the seventh segment, preceded 

 by seven pairs of normal legs, or with some of the anterior legs 

 modified as accessory organs. 



Three suborders of Coelocheta are recognized, the Chordeumoidea, 

 the Striarioidea, and the Lysiopctaloidea, the last containing a single 



