232 Zoology of Colorado 



pressed many-segmented body. They live in salt and fresh water, 

 and in Japan I observed a terrestrial species. Ours are found 

 in mountain lakes, the Gammarus limnaeus of S. I. Smith being 

 common. Miss Rathbun informs me that two other species of 

 Amphipoda, Differ ogammarus fasciatus and Eucrangonyx gracilis, 

 are represented by Colorado specimens in the U. S. National 

 Museum. 



The Isopoda are the so-called wood-lice and pill-bugs, terres- 

 trial animals common under stones. Armadillidium vulgare, the 

 European pill-bug, was abundant in a greenhouse at Boulder, of 

 course introduced. When alarmed, it curls up in a ball, hence 

 the generic name, meaning like an armadillo. The wood lice 

 found out-of-doors also appear to be species introduced from 

 Europe. 



The Ostracoda, living in fresh waters in great abundance, 

 are small creatures enclosed in a carapace which has the form of 

 a bivalve shell. It would be easy to mistake them for small 

 molluscs. As the little shells are easily preserved, they often 

 occur as fossils, and one species (Cypris florissantensis) is common 

 in the Miocene shales at Florissant. Professor A. E. Beardsley 

 of Greeley has long been studying the Colorado Ostracoda, and 

 tells me that he has more species from our State than are at 

 present recorded from the whole United States. 



The Copepoda are very small fresh water Crustacea, without 

 carapace, and without paired eyes. It is the single median eye 

 which has caused the name Cyclops to be given to the genus con- 

 taining the commonest forms. There are two pairs of antennae, 

 and the females carry the eggs in a pair of sacs, one on each side 

 of the abdomen. The largest Colorado genus is Diaptomus of 

 Westwood, with thirteen species, three of which were originally 

 described from Colorado. Some of them are beautifully colored 

 when alive. Some very peculiar Copepoda are parasitic on fishes, 

 and certain of them are quite large. The Order Branchiura 

 includes the genus Argulus, a species of which (A. trilineatus 

 Wilson) was found on a gold-fish in Boulder by Mr. Guy Mason. 

 It has round adhesive discs on the under side of the body, and the 

 tail is deeply notched. 



The Cladocera or water fleas are something like the Ostra- 

 coda, but with a clearly visible external head and distinct paired 



