MEMOIES OF THE NATIONAL ACADEMY OP SCIENCES. 



33 



these species inhabit, they appeared at the surface in springs, and even at the mouths of tile 

 draius, in such numbers that a hundred could be taken in an hour. A few females were observed 

 with eggs at this time (July)." 



Upon the whole, the Illinois specimens are the most aberrant, i. e., the farthest removed from 

 Asellus communis, of any forms found in Mammoth or other eaves. They are more linear than 

 some specimens taken from wells in Anuville, Lebanon county, Pennsylvania, kindly sent us by 

 Mr. L. H. McFadden, who writes me that they also occur in the springs and wells in the limestone 

 rocks of Cumberland and York counties. 



The Pennsylvanian examples were large and well developed ; the females were 16 mm in length; 

 and the greatest width, 4 mm ; length of first antennas, 3 mm ; of second antennas, 15 mra , or almost as 

 long as the body itself. The first antennas were large, well developed, and sixteen to seventeen 

 jointed. PL III, figs. 4; 4a represents the end of the antennule, showing three olfactory rods arising 

 from the sixth joint from the end, this being probably an anomaly.* 



Ccecidot^sa nickajackensis Packard. PI. Ill, figs. 9, 9a. 



Ceecidotcea nickajackensis Pack., Amer. Naturalist, xv., 879, November, 1881. 



Body longer, narrower, and slenderer than in G. stygia. The antennae are sometimes very 

 long, and reach to the end of the third joint of the second antennas; they are sometimes nearly 

 twice as long as in C. stygia, and are purplish-white, while the flagellum is provided with long 

 hairs. Figs. 9, 9a, however, represents a short first antenna composed of 

 only 8 to 9 joints with a single long olfactory rod on the sixth joint. 



The second antennas are as loug as the head and extend back- 

 wards as far as the base of the abdomen. The legs are much longer 

 and slenderer than in C. stygia. The abdomen is long and narrow, 

 and the caudal appendages are moderately long in one specimen and 

 short in another; in one individual the outer branch is much shorter 

 and smaller than in the others, and in most it is as long as the basal 

 joint. On the whole, the caudal appendages are no longer than the 

 telson or terminal segment of the abdomen, while in G. stygia they 

 are half as long as the entire body. 



This species forms, in the antennas and slightly purplish color 

 and the proportions of the leg-joints, perhaps a nearer approach to the 

 genus Asellus than that of Mammoth and Wyandotte caves; on the 

 other hand, G. stygia approaches Asellus more in its shorter, broader 

 body, with the shorter, broader abdomen. It seems quite evident that 

 the two species must have descended from different species of Asellus. 

 Whether there is an additional species in the Southern States from 

 which tbe present species may have been derived remains to be seen. 



The two specimens from Lost Eiver, found by Dr. Sloan iu that 

 subterranean abode, were of the normal form and size of A. communis, but bleached as white as 

 G. stygia; the eyes are black and distinct. This variety may be called pallida. It is interesting 

 to note the occurrence of tliis bleached variety, which may have become thus modified after but a 

 few generations; perhaps but one or two. 



Besides Asellus communis, which is widely diffused throughout the Eastern and Central States, 

 Mr. Forbes has described two species which occur in southern Illinois, neither having been 

 detected in central or northern Illinois, although the most varied situations were carefully searched. 



Our sketches (PI. IV, figs. 3, 3a-3g) will give some of the details of structure of A. communis, 

 which will serve as a basis of comparison. 



Asellus intermedins Forbes, Bull. 111. Mus. Nat. Hist., No. 1, 10. 

 This species, as remarked by its describer, is intermediate between Asellus communis and 

 A. brevicauda. As will be seen by reference to Forbes' Fig. 14, the caudal stylets are like those of 



* The auditory bristles of this species were mistaken by Mr. Hubbard for "an unknown ciliate Infusorian?" 

 See bis Fig. 106, aud Amer. Ent., iii, p. 80. 



S. Mis. 30, pt. 2 2 



FIG. 7. — Ccecidotcea nickajackensis •, 

 Pack, a, antennule; 6, caudal stylets; 

 all enlarged. 



