436 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxv. 



caused by raising- the stone had cleared awa}', they could be seen lying 

 quietly in their cavity or treading the mud to avoid being covered up. 

 They were easily caught in the hands, as even after they had been 

 touched they made no great effort to get out of danger. Indeed, in 

 one case, I let a large specimen drop back into the water and a minute 

 or so later found it \y'\ng at my feet; it had sunk like a stone and had 

 not tried even to crawl away. They seemed to be totally devoid of 

 the senses of sight and hearing, and the sense of touch did not seem to 

 be nearly as well developed as in C. pellucidus. I tried many experi- 

 ments to determine these points, as well as those regarding the habits 

 mentioned above. As is well known, C. hmnulatus differs considerabl}^ 

 from C pellucidus and is more closely related to such forms as C. har- 

 tord or C. latimanus, which are surface dwellers and provided with well- 

 developed eyes. Nevertheless, the general appearance is so strikingly 

 like C. pdlucidus that without a careful examination it would be exceed- 

 ingly difficult to distinguish the two species. Compared with the two 

 other blind crayfishes from this country, 61 setosus and C. acherontls^ 

 the resemblance is less marked and the greatest difference is noticed 

 between C. hamulatus and C. setosns. Yet C. setosus is the closest 

 relative of C. /lavifdatus, while C. pellucidus and O. acherontis, which 

 are very dissimilar in general appearance, are closely related. These 

 facts are cited to show that there are apparently certain characters in 

 the Crustacea which readily lend themselves to modification under sub- 

 terranean influences, but which mean very little when it comes to detect- 

 ing family, generic, or specific relationships or differences. Sense 

 organs and color ma}^ change with such rapidity that the animal becomes 

 a true spehean species before it is able to so change its habits as to 

 become perfectly adapted to a subterranean life. Thus, I would regard 

 the haliit of living under stones of C. hamulatus and Owcidotea ricli- 

 ardsonx as a primitive instinct to which the animals cling in spite of 

 the fact that it is useless. C. 2)clUwidus is probably an older species 

 and has adapted itself more perfectl}^ to conditions in the caverns 

 where no special concealment is necessary. 



As to the ancestry of C. hamulatus we would most willingly look to 

 some species of the C. hartoni group, which occurs in this region, and 

 of the three which are known to occur, C. hartoni^ C. latiinanus^ and 

 (■. extraneus^ the latter is far more like C. hamulatus than either of the 

 other two. There is, however, another species, Cjordani Faxon, which 

 in .some characters agrees still more closely with 0. /tarjiulatus, and its 

 i-ange is not so far away as to make it impossible that it will still l)e 

 found in the same territor3^ The wide and long areola, the lateral and 

 l)ranchiostegial spines of the carapace, the ffat rostrum with lateral 

 spines and long acumen, triangular epistoma. long antenna? (even 

 longer va jordani than in hainulatus), the shape of the antennal scale, 

 the development of hair on the inner faces only of the third maxilli- 



