MILLIPEDS OF FAMILY LYSIOPETALIDAE — ^LOOMIS 117 



TYNOMMA, new genus 



Type. — Tynomma sedecimum, a new species from California. 



Diagnosis.— This genus is related to Spirostrephon and Diactis 

 but has genitalia dissimmilar to both. The smaller size ; smaller eye 

 cluster; and the greater differentiation of the primary and sec- 

 ondary crest of the anterior segments also distinguish it from 

 Spirostrephon, while externally it differs from Diactis by the smaller 

 eye cluster; the nearly parallel inner primary crests of segments 

 2, 3, and 4 ; and the normal coxae of the seventh male legs and all 

 legs near the middle of the body. 



Description.— Body rather slender, 14 to 15 times as long as broad, 

 moderately depressed in both sexes ; segments 46 to 53 in number. 



Eye cluster relatively small, containing 22 to 39 ocelli in 6 to 8 

 rows, as counted downward from the top of the head; sense organ 

 moderately large and occupying more than half of the distance be- 

 tween the eye and the base of the antenna. 



Antennae resembling those of Diactis in shape and proportions. 



First segment of the usual shape, with 16 to 18 distinct crests, 

 the inner ones of two sizes like the crests of segment 2, except that 

 between the inner pair of primary crests there are no secondary 

 ones; lateral crests large and resembling the inner primary crests, 

 except that they are longer and cross the posterior two-fifths of the 

 segment. In front of the crests is a triarcuate series of 10 setae, 

 the fourth seta on each side, counting inward, set far behind the 

 third and fifth setae. 



Segments 2, 3, and 4 with the inner pair of primary crests almost 

 parallel, not strongly divergent as in Diactis but more oblique than 

 in Spirostrephon. 



Transition to the full number of dorsal crests occurs on segment 

 11 or 12. 



Primary crests thin and with the apex smooth; the sides of all 

 primary and secondary crests and the surface between them uni- 

 formly reticulated. 



Secondary crests reaching the posterior margin of the segments, 

 the crests less conspicuous on the caudal segments. 



Poriferous carinae not much more prominent than the primary 

 crests of the dorsum; lateral margin of the carinae completely oc- 

 cupied by the rather broad poriferous impression, except on several 

 of the first poriferous segments where it does not extend to the 

 posterior corner. Below the carinae are two primary crests, which 

 are larger and more conspicuous than the dorsal crests. 



Last segment narrowly rounded-truncate behind and with six 

 setif erous tubercles in addition to the apical papillae. 



