162 



BULLETIN UNITED STATES GEOLOGICAL SUEVEY. 



Pig. 6. — Polydesmus cavicola, Pack., 



n. sp., (enlarged.) of tubercleS 



ratus^ P. granulatus, or P. canadensis. The median suture is well 

 marked. Though like the other species of the genus and family it is 

 blind, the hexagonal markings which indicate the normal position of 



the eyes are nearly as distinctly marked as in 

 P. canadensis. Antennae rather longer than in 

 P. canadensis, being twice as long as the head, 

 7-jointed, — the first, as usual, conical, small, 

 and short; second and third oval cylindrical, 

 of the same form and length ; fourth* and fifth 

 considerably shorter (three-fourths) than the 

 second and third, the fifth a little thicker than 

 the fourth; sixth much thicker and more spher- 

 I ical than in any other species of Polydesmus 

 figured by Wood or known to me ; seventh 

 joint small, conical, a little more than half as 

 long as the sixth. They are pubescent, with 

 scattered, stiff hairs. The first segment behind 

 the head is crescent-shaped, but little more than 

 half as wide as the head, bearing two rows 

 The remaining joints from the 

 fourth backward are about half as long as broad, with three rows 

 of conical tubercles, those in the hindermost (third) row the largest ; 

 the sides of each segment emarginate, and produced posteriorly into 

 a large spine, much as in P. canadensis. Terminal segment conical, 

 ending in a conical, pointed, curved spine, and bearing a large spine on 

 the side. Body covered with fine hairs. Legs as usual, 6-jointed; the 

 fourth and fifth joints taken together as long as the sixth, which Is 

 slender, very hairy, ending in a long spatulate claw. Color uniformly 

 pale white, including the head and appendages. Length, 5 millimeters. 

 It differs from any other American species known to me in its large 

 round head, which is much wider than the body, in the' unusually cylin- 

 drical body, with the three rows of conical papillee or spines, and the 

 swollen sixth antennal joint. It is allied in the granulated and narrow 

 hodj to P. granulatus, hnt in the emarginate and posteriorly-produced 

 segments to P. canadensis, but differs from both as well as Say's P. 

 serratus in the much narrower, more cylindrical body, as well as in the 

 proportions of the joints of the antennae. Thus far no species of Poly- 

 desmus has occurred in Utah, so that a careful comparison with more 

 closely-allied forms than those mentioned has not been possible. Four 

 examples occurred under stones in a damp spot in Clinton's Cave, Lake 

 Point, about twenty miles west of Salt Lake City, Utah. 



So far as these specimens prove anything, the results of a life in 

 almost total darkness upon this Myriopod are seen in the antennae 

 being a little longer than in allied forms and in the hairy, attenuated 

 body. That it is a descendant of some out-of-door form is attested by 

 the large, well-marked tubercles on the body, like those in P. granulatus^ 



