FLOATING CRAB. 137 



The carapace in the largest specimens in my possession, 

 which are from the gulf-weed floating in the Atlantic, is 

 eight-tenths of an inch long, and the same broad : the 

 females being smaller than the males. In the British 

 specimens the length and breadth does not exceed four- 

 tenths of an inch. 



The occasional occurrence of this erratic species on our 

 southern coast enables me for the first time to give it a 

 distinct place in our British Fauna. There are in the 

 British collection of Crustacea, in the British Museum, three 

 specimens, placed there by Dr. Leach, obtained, as I 

 believe, from the coast of Devonshire ; and Mr. Couch, in 

 his Cornish Fauna, has the following notice of another : 

 " A species of the genus Grapsus is in the Athenseum at 

 Plymouth, under the name of G. pelagicus, by Mr. 

 Prideaux, and known to Dr. Leach. It is understood that 

 the collection in the Museum of that Institution is con- 

 fined to specimens taken on the borders of Devon and 

 Cornwall/ 1 I have also received from this gentleman, 

 whose diligence and tact in observing facts in Natural 

 History is equalled by his kindness and liberality in im- 

 parting his information, a very young specimen from the 

 Cornish coast, which is extremely small, being not more 

 than a line in breadth. It was sent to me with some 

 other specimens of various very small Crustacea, apparently 

 taken from sea-weed ; it is quite perfect, although so small, 

 and is of a very pale grey colour, with small dark dots. 

 Such is the amount of our knowledge of this species as an 

 inhabitant of our coasts. 



The several species are found in great numbers on the 

 sargasso or gulf-weed, amongst which they breed, live, and 

 die. One species is particularly mentioned by Sloane in his 

 Natural History of Jamaica, as being found on the Sargasso 



