A. E. Verrill — Species of Grapsoid Crustacean. 11.9 



Art. XIV. — Notahle Case of a Species of Grapsoid Crus- 

 tacean apparently in actual process of Evolution',* by 

 A. E. Verrill. 



[Brief Contributions to Zoology from the Museum of Yale University — lxviii.] 



While collecting Crustacea, etc., in Bermuda during the 

 spring of 1901, I was particularly interested in a grapsoid 

 crab of the genus Sesarma, which has acquired terrestrial 

 habits in a remarkable degree, as compared with the most 

 nearly allied form (S. Jiicordi), which lives on the adjacent 

 shores, at about high-tide level. 



The large genus Sesarma is distributed all around the 

 world in the warmer latitudes. There are about twenty 

 American species. All the species have a broad network of 

 hairs on the external under surface of the branchial areas, for 

 the purpose of purifying and aerating the water used in the 

 branchial cavity to keep the gills moist. The length of time 

 that they can remain away from a supply of water largely 

 depends, therefore, on the size of the branchial cavities and 

 the extent of the external aerating areas. Many species never 

 live away from the sea shore. Some, like the S. reticulatus 

 of the Atlantic coast, from Connecticut to Florida, live in 

 holes in wet salt marshes, associated with "fiddler- crabs," their 

 holes descending to permanent water level. Others, like S. 

 cinerea of the Carolina coasts, live just above high-tide level, 

 hiding under stones, driftwood, lumber, etc. Several species 

 in the tropics live among the tangled roots of mangroves, in 

 the swamps, mostly just above high-water level, but within 

 easy reach of water. Some species, like S. Roberti, of the 

 Antilles, have acquired more arboreal habits and climb into 

 the upper branches of trees, often going far away from water, 

 especially in those islands having abundant rains.t 



The common species in Bermuda (S. JRicordi) lives ordi- 

 narily at and just, above high-tide level, within easy reach of 

 water. It is often seen running actively about among the 

 stones and dead seaweeds, usually associated with Pachygrap- 

 sus transversus. It may almost always be found under masses 

 of Sargassum cast up on the shores, as well as under stones. 



* Abstract of a paper read before the American Society of Naturalists, 

 Dec. 27, 1907. For illustration see Trans. Conn. Acad. , vol. xiij, plate x, fig. 8. 



f My son, Mr. A. H. Verrill, who collected this species in Dominica 

 Island, states that while riding along the roads he often took it from 

 the overhanging branches of trees ; others were taken from the branches of 

 fruit trees. This species has a very large branchial chamber. 



