Crustacea 233 



eyes. The large branched antennae are used in swimming. 

 Thirty-four Colorado species are known. 



The Conchostraca have a comparatively large bivalved shell, 

 one of our species (Esther ia morsei of Packard) being 10 to 12 mm. 

 long. The genus Estheria, with 18 to 22 concentric lines of 

 growth on the shell, is easily recognized. It is often abundant 

 as a fossil; I found it in quantity in rocks of Rhaetic age near 

 Mendoza, Argentina. The species of Estheria may be found in 

 pools on the plains, as at La Junta, Fort Collins and Greeley. 

 Eulimnadia texana of Packard, with only five lines of growth on 

 the shell, was taken at La Junta. 



The Notostraca, relatively large animals with a shield-like 

 carapace, and a many-segmented abdomen projecting behind, 

 also occur in isolated pools. At the end of the abdomen are two 

 slender tails. The commonest genus is Apus, but we also have a 

 genus Lepidurus, recognized by the paddle-like process at the end 

 of the abdomen, between the caudal filaments. The genus Apus 

 (Apus obtusus James, 1823) was first observed in Colorado by 

 Long's Expedition in rain water puddles near the Platte River. 

 It appears to be the same species as that much later called A. 

 longicaudatus by LeConte, based on specimens from near Long's 

 Peak. Mr. H. C. Markman found it abundant in a road-side 

 pool at Montclair, near Denver. The sporadic occurrence of 

 Apus has frequently been commented upon. It will suddenly 

 appear in abundance in rain-pools, and may not be seen again 

 for a long while. In England, Apus cancriformis was formerly 

 found in several places, but for over forty years none were seen 

 in the British Isles. Then, in 1907, it reappeared, specimens 

 being found in the south of Scotland. How did they get there? 

 It is known that the eggs are not killed by drying, and they may 

 readily be carried in mud on the feet of wading birds, which fly 

 for long distances on migration. Thus it is possible for Apus 

 to spread, and appear where it was long unknown. Also, the 

 eggs apparently survive in the mud of dried-up pools for a long 

 time, permitting the development of the adults when circum- 

 stances are favorable. 



The Anostraca or fairy shrimps are sometimes over an inch 

 long, slender-bodied, without any carapace. The segmentation 

 is very distinct. These also occupy temporary pools, often in 



