6 BULLETIN 129, UNITED STATES NATIONAL MUSELTm 



disguise, the crab having the same appearance as its environment.^ 

 Among the genera most commonly decorated are Libinia, the shore 

 crab of the eastern coast of the United States, the various species of 

 Hyas, and Oregonia. The members of the Acanthonychinae are less 

 likely to be obscured than those of the other subfamilies, on account 

 of their smoother carapaces. 



The Parthenopidae are relatively few in number of specimens as 

 well as species. Their appearance is so different from that of the 

 Majidae that they can be distinguished at a glance. They are usually 

 small; the largest ones in American waters do not exceed 4 cm. in 

 carapace-width, with the exception of Aethra which attains a width 

 of 9 cm. The carapace is in general broad-triangular or pentagonal 

 with angled corners and facets. The smoother sorts resemble small 

 chips of stone while the tubercled and eroded species simulate rock 

 surfaces. Hooked hairs are nearly always absent. The ambulatory 

 legs are usually small and delicate, the chelipeds immensely long and 

 heavy in American species, the elongate hand terminated by short 

 fingers. The Parthenopidae differ from the Majidae also in having 

 small, complete orbits and an insignificant basal antenna-segment 

 which is not soldered to the epistome or front. They incline toward 

 the Brachyrhyncha.' 



The Hymenosomidae form a small family, the species inhabiting 

 chiefly the southern hemisphere, India, or Japan. They are small 

 marine or estuarine crabs, with a thin, flat, triangular or subcircular 

 carapace. Only one species is American, distributed in southern 

 Chile, Patagonia, and various subantarctic islands eastward to New 

 Zealand. This family is by many authors associated with the 

 Grapsoid crabs,^ but is included here chiefly on account of the form 

 of the outer antennae, the longitudinal position of the antennules, the 

 presence of a rostrum, and the absence of orbits.^ 



' For details of methods and motives, the following works should be consulted; 



Aurivillius, Carl W. S.: Die' Maskirung der Oxyrrhynchen Dekapoden. K. Svenska Vetensk.-Akad. 

 Handl., vol. 23, Stockholm, 1889, 71 pp., 5 pis. 



Pascoe, Francis P.: Foreign Substances attached to Crabs. Nature, Dec. 26, 1889, p. 176. 



Garstang, Walter: Foreign Substances attached to Crabs. Nature, Mar. 27, 1890, p. 490. 



Bateson, W.: Notes on the Senses and Habits of some Crustacea. Journ. Marine Biol. Assoc. United 

 Kingdom, n. s., vol. 1, No. 3, Apr. 1890, pp. 213-214. 



Stebbing, Thomas R. R.: A History of Crustacea. The International Scientific Series. New York, 

 1893. Pp. 112-116. 



Sayce, O. A.: Some peculiar Habits of Crabs. Victorian Naturalist, vol. 17, Melbourne, 1900, pp. 74-75. 



Minkiewicz, Romuald: The Instinct of Self-Concealment and the Choice of Colors in the Crustacea. 

 Rev. gto. Sci., Paris, 20th year. No. 3, Feb. 15, 1909; Transl. in Smithson. Rept. for 1909 (1910), pp. 465-485. 



Pearse, A. S.: The Influence of Different Color Environments on the Behavior of Certain Arthropods. 

 Journ. Anim. Behavior, vol. 1, No. 2, 1911, pp. 79-110. With bibliography. 



Milligan, H. N.: The Habits of the Four-horned Spider Crab. Zoologist, ser. 4, vol. 19, 1915, pp. 248- 

 252. 



Nininger, H. H.: Crabs taken at Laguna Beach in the summer of 1916. Pomona College Journ. Entom i 

 and Zool., vol. 10, No. 2, June, 1918, pp. 36-42. 



' See Ortmann, Zool. Jahrb., vol. 7, Syst., 1893, p. 412. 



• See Alcock, Journ. Asiat. Soc. Bengal, vol. 69, 1900, pp. 280, 282, 285, 291, and 385. 



• See Ortmann, Bronn's Thier Reich, vol. 5, pt. 2, Arthropoda, 1898, p. 1168. 



