208 A HISTOKY OF KECENT CEUSTACEA 



posterior face of which there is a pit or depression, an 

 arrangement designated by Dr. Hagen as the annulus 

 ventralis. Mr. Faxon enumerates no less than fifty-five 



B t/ 



species, twenty-one of them being described by him as new 

 in 1884. Gambarus Diogenes, Girard, which is widely 

 distributed in the United States, constructs curious 

 ' chimneys ' at the mouth of its burrows, and Gambarus 

 dubius, Faxon, it is said, ' makes tnud chimneys like G. 

 Diogenes, which it seems to represent in the mountain 

 regions, G. Diogenes belonging to the low lands.' Gam- 

 barus argillieola, Faxon, is closely related to the two pre- 

 ceding species. The types of it were dug out of burrows 

 in solid blue clay in Detroit, Michigan. ' The burrows- 

 were three to five feet deep. At the bottom of each 

 burrow was a pocket in a layer of loose gravel and clay, 

 holding water. Just above the water-line an enlargement 

 in the burrow formed a shelf on which the animal rested/ 

 It is a pleasing picture of retirement, safety, and comfort, 

 if one can accommodate one's mind to the feelings and re- 

 quirements of a crayfish. Gambarus pellucidus (Tellkainpf) 

 is the blind species of Mammoth Cave, Kentucky, in which 

 it is noticed as a singular circumstance that Gambarus: 

 Bartonii (Fabricius) occurs with well-developed eyes. 



Cambaroides, Faxon, 1884, is only introduced by its 

 author as a sub-genus of Potamobia, but it may as well 

 follow its destiny at once and become a genus. Huxley in 

 'The Crayfish' mentions Astacus dauricus, Pallas, and 

 Astacus Schrenkii, Kessler, as restricted to the basin of the 

 Amur, which sheds its water into the Pacific over against 

 Japan. He points out that the branchial system of the 

 Amurland Astaci is apparently the same as that of the rest 

 of the genus, but that the second and third trunk-legs in 

 the male have a hook-like process on the third joint, and 

 that the females have the transverse prominence already 

 noticed in Gambarus. It is on this combination of charac- 

 ters from Cambarus and Potamobia that Faxon has founded 

 his Cambaroides, to include the two species just mentioned 

 and the Astacus japonicus of de Haan. In this species he 

 suspects the existence of two forms of the male, a pecu- 



