CRAB GENERA PLANES AND PACHYGRAPSUS — CHACE' 79 



the U. S. National Museum is a specimen of Portunus (Portunus) sayi 

 (Gibbes) that bears the same locaUty data, and this crab is otherwise 

 rehably reported only from the Atlantic. Examination of additional 

 material from the Indian Ocean will be necessary before it can be 

 definitely ascertained whether one or both species occur there. The 

 fact that Alcock (1900) recorded no specimens of the genus indicates 

 that it is not a common component of the Indian fauna. 



One of the most interesting aspects of the distribution of Planes is 

 its apparent absence from the Gulf of Mexico west of the Dry Tortugas 

 despite its relative abundance from the Straits of Florida eastward 

 and its occurrence in the Caribbean area. Joel W. Hedgpeth, of the 

 Institute of ^Marine Science at Port Aransas, Tex., and Dr. Allan F. 

 Archer, of the Alabama Museum of Natural History, inform me that 

 they have never encountered the crab although they have searched 

 through great masses of Sargassum from the Gulf. It would be 

 interesting to know what factor or factors preclude the dispersion of 

 Planes into an area such as this where the presence of floating weed 

 and particularly of sea turtles would seem to afford ideal sources of 

 attachment for the crabs. 



There are likewise very few records of the presence of Planes in the 

 central South Atlantic, possibly because of the comparatively small 

 amount of exploratory work done in that extensive region. If the 

 occurrence of P. minutus in the Indian Ocean is finally confirmed, it 

 would be of considerable interest to know more of the distribution of 

 the genus in the South Atlantic, particularly whether the Pacific 

 P. cyaneus extends into the western part of the South Atlantic and, 

 if it does, whether the ranges of the two species overlap there. Inas- 

 much as Planes is not infrequently found among the under-water 

 growth on ships' hulls and as the crabs are said to be common in the 

 Straits of Magellan (Jacquinot and Lucas, 1853, p. 78), through which 

 much of the steamship traffic passed in the early part of this century, 

 it would be remarkable if intermingling of the two forms had not 

 occurred commonly in the past. 



The known distribution of Pachygrapsus marinus is limited to the 

 records from the coast of Oregon and the Hawaiian Islands, in addition 

 to the type locality west of Baja California; further collecting will 

 probably show its range to be far more extensive in the eastern North 

 Pacific and possibly in the western portion as well. Dr. C. H. 

 Edmondson informs me that, of 18 lots and 150 or more specimens 

 identified as Planes minutus in the Bernice P. Bishop Museum, 3 lots 

 containing a total of 22 specimens are apparently Pachygrapsus 

 marinus and 3 of the remaining 15 lots contain both Planes and 

 Pachygrapsus, including 30 or more specimens of the latter. All the 

 lots containing Pachygrapsus marinus were taken off Oahu. 



