152 NEW YORK STATE MUSEUM 



They are of considerable economic importance, as they frequently 

 occur in immense numbers and are an important, if not the principal, 

 food of many fishes. 



Bate, G. Spenoe. Catalogue of the Amphipodous Crustacea of the British 

 Museum. Lond. 1862. 



Bate & Westwood. British Sessile-eyed Crustacea. Lond. 1863. 



Holmes, S. J. Synopses of North American Invertebrates, 18. The Am- 

 phipoda. Am. Nat. 1903. 37:267. 



Sars's work, mentioned before, is also valuable, as it gives a classi- 

 fication of the group and many figures of species, some of which are 

 found on our shores. 



The Amphipoda are divided among three tribes : 1 Ilyperiidea, 

 2 Gammaridea, 3 Caprellidea. 



The first of these is purely pelagic or free-swimming and its forms 

 generally possess relatively enormous eyes. Specimens have not 

 been taken within the city limits but they probably occur. By far 

 the greater number of species belong to the second tribe, the third, 

 which is of a distinctly degraded type, being a small one. 



2 GAMMARIDEA 

 According to Sars, this tribe is divided into 25 families and of 

 these 7 have common representatives in New York city. 



Family orchestidae 



Antennulae much shorter than antennae and devoid of a secondary 

 flagellum. Mandibles without a palp. Gnathopods variable, the 

 second pair being generally different in the two sexes. First two 

 pairs of uropoda strong, last pair smaller and one branched. 



A very distinct family, the members of which have become more 



or less adapted to terrestrial life. They may be said to be the beach 



fleas. 



Allorchestes dentata (Smith) 



Hyalella dentata Smith, S. I. U. S. Fish Com. Rep't. 1872-73. 

 p.645, pl.2, fig.8-10. 



A fresh-water form in which the first' and second abdominal seg- 

 ments are produced dorsally into spines. 



Much the smaller of the two fresh-water Amphipods found within 

 the city. It also differs from Gamma rus fasciatus, the 



