2 INTRODUCTION. 



The whole collection is now in a safe condition, mostly unpacked and 

 arranged in new alcohol. The division of the entire assemblage has 

 been carried as far as the families, that of the greater part as far as the 

 genera, while several families have been critically identified. There are 

 over four thousand two hundred jars. The number of specimens, per- 

 haps, exceeds sixty thousand ; the additions during the years 1863- 

 1866 were fourteen thousand specimens. According to Professor L 

 Agassiz's estimate, the collection comprises more than two thousand 

 species, the entire number of species as yet known being about five 

 thousand. A closer examination of several families verifies this esti- 

 mate, or rather indicates that it is probably too small. Nearly one half of 

 the collection is formed by the Brachyura, one fourth by the Macroura. 



The value of the collection is the greater from the circumstance that 

 most of it has been secured and formed, in view of a definite plan 

 adopted by Professor L. Agassiz for the purpose of examining and de- 

 fining the different fauna? in the gigantic water-area spreading between 

 the coast of Eastern Africa and Western America. Several persons 

 have been charged with the collecting of the fishes, the Crustacea, and 

 the polyps at chosen points, — at Zanzibar, Mr. C. Cooke ; at Kingsmills, 

 Sandwich and Society Islands, Mr. Garrett ; on the West Coast of Amer- 

 ica, Messrs. A. Agassiz, and T. G. Gary. At the same time rich collec- 

 tions have been received from additional intermediate localities. — 

 Rangoon, Singapore, China, New Holland, and others, chiefly through 

 Captain W. A. Putnam. The Museum is also very rich in specimens 

 from the shores of the United States, from the Antilles, and from 

 Brazil ; it likewise possesses valuable materials from the European and 

 Mediterranean fauna. 



The materials examined by me for this monograph of the North 

 American Astacidae are, I think, as yet unrivalled. They consist of the 

 following assemblages: 1. The Astacidae of the Cambridge Museum, 

 twenty-five species, represented by nearly two thousand alcoholic speci- 

 mens from one hundred and fifty different collectors and as many differ- 

 ent localities, besides some dry specimens, partly types of Dr. Gibbes. 

 2. The Astacidae of the Museum of the Philadelphia Academy, kindly 

 communicated to me by Professor Leidy, containing types of Messrs. 

 John LeConte and Girard. 3. The Astacidae of the Museum of the 

 Natural History Society in Boston, containing types of Professor W. 

 Stimpson. 4. The Astacidae of the Museum of the Peabodv Academy 

 in Salem, which, with the last, were kindly communicated to me by Dr. 



