156 A New Species of Apus. 



served before, it is impossible to determine where it should be 

 arranged. 



* APUS LONGICAUDATUS. 



Pale brown : Luckier large, thin, gibbous, nearly round, carinate 

 on the middle of the back, deeply emarginate behind, the edges of 

 the emargination fringed with short spines : eyes three, simple, the 

 two anterior larger, approximate, somewhat lunate, the third one 

 round, placed in the middle behind the two others : antennas very 

 short, inserted near the mandibles, two-jointed, joints clyndrical, 

 subequat, the second joints somewhat accumulate and naked at the 

 tip : first pair of feet, or as they have been called, exterior anten- 

 nae, furnished with four articulated filaments; of these filaments, 

 the outer one is longer than the body, the next half the length of 

 the first, the third about one third the length of the second, and 

 the fourth very short : the other feet, amounting to ten pair, are 

 flattened, trifid at the tip, the intermediate division being the long- 

 est, furnished ou the inner side with a short branch, and exter- 

 nally with a broad lamina ; below these feet are twelve pair of 

 laminae, the five anterior pair larger, the seven smaller pair reach- 

 ing to the vent, which is covered by the last pair ; these laminae 

 are complicated in their structure, and ciliate with short hairs : 

 tail long, consisting of sixteen joints counting downwards from 

 the vent, the last one the longest, somewhat coriaceous, emargi- 

 nate and ending in two long articulated naked filaments, the joints 

 of the tail and of the filaments are furnished each with a row of 

 small spines, which run entirely round. 



Length to the end of the tail, 1.5 of an inch, of the buckler, 

 .65,' breadth "of the same, 7. 



Plate III., fig. 1. (a.) ono of the feet, (b.) one of the lamina?. 



Of the habits of this animal, we know but little ; it was found 

 in immense numbers in a small shallow lake on the high platoau 

 between Lodge-pole creek and Crow creek, north-east of Long's 

 peak : they were swimming about with great activity, plunging to 

 tli - bottom and rising to the surface. All of them that were caught 

 appear to be males, at least none of them have any ova attached : 

 the common species in Europe, A. cancriformis, on the contrary, 

 has never been found but of the opposite sex. 



