NOTES ON THE CRUSTACEA OF THE TRES MARIAS ISLANDS. 



By MARY J. RATH BUN, 

 Second Assistant Curator, Dirision of Marine Invertebrates, U. S. National Museum. 



Of the four species of Crustacea taken by E. W. Nelson and E. A. 

 Goldman on the Tres Marias Islands in May, 1897, two are identical 

 with forms inhabiting Lower California, one is found in all the warm 

 countries of the world, while the fourth, a fresh-water shrimp, is dis- 

 tributed throughout tropical America. 



Gecarcinus digueti Bouvier. 



Gecarcihus digueti Bouvier, Bull. Mus. Hist. Nat., Paris, I, 8, 1895. 

 Maria Cleofa Island. May 30. One large male (Collectors' No. 717). 



The type and only specimen hitherto collected is from Lower Cali- 

 fornia, and is in the Paris Museum. This species differs from others 

 found on the Pacific coast in its wider carapace, narrower front, longer 

 legs, and in the form of the abdomen of the male. 



Measurements. 



The measurements of the legs are exclusive of the large spines, and 

 the length given is that of the anterior or superior margin. The penult- 

 imate segment of the abdomen of the male is very wide. Length and 

 distal width, 12 mm.; proximal width, 21.5. 



Mr. Nelson says of these crabs : 



On the Tres Marias we found them only on Maria Cleofa, where they were very 

 numerous above high-water mark on the sandy beaches of the low eastern part of the 

 island. They were also living very abundantly in burrows in the soft soil almost 

 everywhere on the slopes of Isabel Island. They are nocturnal in habits, and caused 



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