THE SPIDER CRABS OF AMERICA 



By Mary J. Rathbun 



Associate in Zoology, United States National Museum 



INTRODUCTION 



This volume is the second of the handbooks projected for the 

 study of American crabs, the first volume of which, "The Grapsoid 

 Crabs of America," forms Bulletin 97 of the United States National 

 Museum. The introductory remarks in that bulletin under the 

 headings "Sources of material," "Special researches," "Acknowl- 

 edgments," and "Glossary of terms used" apply also to this bulle- 

 tin. The author has been able to examine much rare and type 

 material at the Museum of Comparative Zoology and the Philadel- 

 phia Academy of Natural Sciences, and a number of photographs of 

 the same have been contributed by those museums through the 

 courtesy of Mr. Samuel Henshaw and Dr. H. A. Pilsbry; while Dr. 

 W. T. Caiman of the British Museum has furnished a photograph 

 of the type-specimen of Lambrus crenatus Wliite, wliich is here repro- 

 duced. I am constrained to acknowledge also my indebtedness to 

 my various colleagues in the United States National Museum who 

 have assisted in getting this volume into shape for publication. 



EXPLANATION OF MEASUREMENTS AND ABBREVIATIONS USED 



Explanation of measurements 



The length of the carapace, unless otherwise stated, is measured 

 on the median line, from the anterior to the posterior margin. 



The width of the carapace is measured at the widest part. 



The fron to-orbital width or exorbital width is measured from the 

 outer angle of one orbit to the outer angle of the other. 



The length of the rostrum in the Majidae is usually measured to 

 the angle which it forms with the orbit ; in the Parthenopidae and 

 Hymenosomidae it is measured from the tip to the posterior line of 

 the upper margins of the orbits. 



The width of the rostrum is measured at its posterior end. 



The length of the segments of the chelipeds and legs is measured on 

 the upper or anterior margin. The length of the whole cheliped or 

 leg is measured on the lower margin, from the articulation of the 

 coxa with the sternum to the tip of the dactylus. 



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