62 MEMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 



Var. carterensis. A decided approach to S. lactarius is seen in certain brown specimens, only partly bleached 

 found in the Carter caves, Kentucky, viz: Bat Cave, X Cave, and Zwingle's Cave, besides a cave across the road 

 from the hotel, which is used as an ice-house. 



In the specimens from Bat Cave the antennae are slightly shorter, and a little slenderer, particularly joints 3 to 

 5; but joint 7 is much shorter and blunter than in the Bradford Cave individuals; the antennae, however, are of the 

 same length, though slenderer than those living in Great Wyandotte Cave. The eyes form a nearly equilaterally 

 triangular area, with from twenty-three to twenty-five facets. The segments behind the head are 30. They differ 

 from the Wyandotte examples in the posterior or swollen portion being rather more prominent than in the former, 

 forming more marked lateral swellings, with about eight ridges on the side of each boss, and the body is larger and 

 thicker, but the legs are of the same length. 



The head is dark in front, mottled above and below with paler horn color. The antennae are concolorous with 

 the head and body, but the terminal joints are paler, as are the legs, which are also paler at the articulations. The 

 entire body is dark horn-brown, mottled and irregularly lineated. 



The smoother anterior portion of the scuta shows a tendency to be paler than the tuberculated portion, and of a 

 bluish-gray tint. The tubercles are no more prominent than in the Wyandotte individuals. 



The segments in both the Wyandotte species and var. carterensis rapidly decrease in size, the penultimate 

 segment being pointed, and each segment is provided with regular, high-raised, parallel, prominent ridges on the 

 shoulder or lateral boss ; about forty to forty-five on a scutum on the sixth segment from the end of the body. 



Length, 23 mm ; thickness, 2.5 mm ; the body being considerably larger and thicker than in the Wyandotte 

 specimens. (See figs. 2, 2a-2e.) 



Two specimens from X Cave are exactly in size and color like those from Bat Cave. 



Three specimens from the ice-house cave only differ from those in Bat Cave in being somewhat paler, but the 

 eyes and antennas are the same. 



A large and a partly grown one from Zwingle's Cave was collected by Mr. Sanborn August 23; these were 

 also paler than those from Bat Cave. With them were associated a Ceuthophilus, with eyes well developed, and 

 a Polydesmus. 



This form or variety would be, perhaps, mistaken for Lysiopetalum lactarium, but it is true in all the generic 

 details to Pseudotremia ; at the same time it is what may be called a twilight species, living in small caves in 

 situations partially lighted. It is probably derived from L. lactarium, or a closely-allied species. We doubt if it will 

 ever be found living in the same situations as L. lactarium. 



It is evident that the var. carterensis is the ancestral form of the now fixed species P. caver- 

 narum, and that the former has been derived either from L. lactarium or from an allied species; 

 hence the genus Pseudotremia has been probably derived from the genus Lysiopetalum, and was at 

 first represented by carterensis, the latter being a twilight species, which gave origin to the 

 cavernarum. We regard this series as the best and clearest proof of the derivative theory which 

 we have observed, proof so clear as to amount almost to a demonstration of species- and genus- 

 making by a change in the environment. 



In Mr. Hubbard's collection from Wyandotte Cave (Aug., 1885) I found a single carterensis considerably larger 

 than any from the Carter Caves, but the body and tips of the antennae are perhaps a shade paler. The eyes are 

 normal, black, while the two last joints of the antennae are a little slenderer than in my types of var. carterensis, but 

 the last joint is decidedly shorter than in the form cavernarum; the specimen is much larger than any P. cavernarum 

 from Wyandotte Cave. 



Genus Scoterpes Cope. 



Spirostrephon (Pseudotremia) Pack., Amer. Naturalist, v, 748, December, 1871. 



Scoterpes Cope, Amer. Naturalist, vi, p. 409, 414, July, 1872. 



Scoterpes Pack., Proc. Amer. Phil. Soc. Phila., xxi, 192, 1883. 

 Body very long and slender, not fusiform ; consisting of thirty segments besides the head, and with about fifty- 

 two pairs of legs, with the penultimate joint very long. Head rather large and unusually broad; no eyes present ; 

 the genae unusually large, extending high up on the vertex, but not so globose as in Trichopetalum ; the front is also 

 carried farther up on the vertex than usual, and is much broader than long ; the clypeus flat, slightly bilobed on the 

 front edge. The antennae are moderately long and hairy, with the sixth segment scarcely longer than in Trichope- 

 talum, but more uniform in thickness, scarcely longer than thick ; the terminal joint as long as the sixth, the end 

 conical, more produced than in Trichopetalum or Zygonopus ; at the tip are four rather long sense-setae. Body seg- 

 ments becoming, as usual, smaller next to the head ; the anterior of each division of the arthromere much swollen 

 high up on the sides ; each shoulder with three tubercles, which are arranged in a scalene triangle and bear much 

 longer setas than in the other genera, though not quite so long as the body is thick. The legs are long and slender, 

 much more so than in Trichopetalum, and somewhat more so than in Zygonopus. In the male the eighth pair of legs 

 are rudimentary, being two-jointed, the second joint only one-fourth longer than the basal, and ending in a well- 

 developed stout claw. The genital armature minute and very rudimentary, pale, scarcely chitinous ; the outer lamina 

 short aud thick, with a stout external recurved spine, and two terminal obtuse points; the inner lamina shorter f 



