MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 31 



Another point of interest is, that we should naturally expect that the abdomen (telson) in the 

 blind European forms would be longer than in our American Caecidotaea, as the abdomen iu the 

 European Aselhts aquations has a telson slightly longer than in the American Asellus communis ; 

 moreover, the legs of the former are longer; the antennae much longer, as well as the caudal stylets, 

 and yet the European blind forms do not exaggerate any of these features of the eyed Asellus, from 

 which they have originated, while the American species do. 



Specific characters. — Normal and well-developed male and female from Mammoth Cave. Body 

 long and narrow; head about as long as broad or slightly narrower than long, much narrower 

 than the first thoracic segment, the latter not so wide and one-fourth longer than the second seg- 

 ment, which is crescentiform ; third slightly shorter but like second segment in shape; fourth a 

 little shorter than third segment, and fifth shorter than fourth and considerably shorter than the 

 sixth ; the seventh a little longer than first and considerably longer than sixth ; the spaces between 

 the thoracic segments large and deep. Abdomen nearly as long as the fifth to seventh, or last 

 three thoracic segments; not quite but almost as wide as the thoracic segments; end of telson a 

 little full in the middle. 



First (smaller) antenna?; in large slender specimens total number of joints, twelve; in shorter 

 less-attenuated females there are eleven to twelve joints. The proportions of the different joints, 

 their relative length and size, do not essentially differ from those of A. communis, except that the 

 two terminal joints are apt to be smaller, though the individual differences are marked, the joints 

 being shorter in short-bodied than long-bodied individuals; so also the setae vary in number and size ; 

 they are arranged much as in A. communis. Olfactory rods, usually three in number, situated on 

 the three penultimate joints, like a cricket-bat in shape, rather more contracted at base, forming a 

 cylindrical handle, than in A. communis ; of the same size as in A. communis — certainly not smaller 

 Owing to the usually much smaller size of the terminal joint the terminal olfactory rod is two to three 

 times as long as the last joint, and the second rod is sometimes longer than the two terminal joints 

 of the autenna collectively. Sometimes there are five olfactory rods (Fig. 8a). The auditory 

 bristles {Setce auditorice, Fig. 2 e, d.s) do not present any specific characters either in form or arrange- 

 ment; there is a short oue on the outer side at the end of the basal joint and three longer ones on 

 the end of the second joint, oue external, the other two internal. In A. communis one occurs at the 

 end of the short fourth antennal joint (Fig. 3b). This has not been yet observed in Cwcidotwa 

 stygia. (The variations in the shape and number of joints are noticed further on.) 



Second antennae with the four basal joints short, third longest of the four and scarcely longer 

 than thick ; the fifth and sixth very long, the sixth over one-third longer than the fifth; the remain- 

 ing joints of the flabellum, eighty-five or less, the number variable; the joints frequently bearing 

 single setae. 



The mandibles differ decidedly from those of Asellus communis; they are more triangular or 

 pointed in the right (PI. IV, fig. 1ft) ; the teeth of the cutting-edge are very unequal, while the setose 

 edge within the teeth is much more parallel with the outer edge of the mandible; the 2 jointed 

 inner lobe is broader and with stouter longer setae; the left mandible is longer and narrower. The 

 palpi are three-jointed; second joint about half or one- third as thick as in A. communis, but the 

 arrangement of the seta' nearly the same; third joint much as in A. communis, equaling in length 

 the basal joint of the palpus, and with two terminal claws. The lobes iu front of first maxilla?, 

 forming the so-called under lip (PI. Ill, fig. 2h), are provided with narrower lobes than in A. 

 communis. The first maxilke (PI. Ill, figs. 2e, 2/), with the outer lobe a little narrower at base 

 but broader at the end than in .1. communis; the terminal spines of the outer lobe much slenderer, 

 more hair-like than those of the inner lobe (Fig. 2/), which are spinulate, and much as in A. com 

 munis. 



Second maxillae (PI. Ill, figs. 2g, 2h,) much as in A. communis, the two outer lobes with the inner 

 stout seta? curiously denticulated on the inner edge; the hairs on the innermost lobe much longer 

 and denser than in A. communis. 



The maxillipedes (PI. IV, figs, lb, lc) differ from those of A. communis mainly in the two 

 terminal joints of the palpus ; the fourth or penultimate joint is iu Cwcidotcea stygia slender and 

 about half as thick as in Asellus, but the terminal joint is a little shorter; the laferal lobes are 

 much more full and rounded where the setae are longest than in Asellus communis. 



