faces of algae and land plants. Usually the crab carapace was prepared for ashing without any attempt to scrub or scrape the surface. In one instance, however, one half of the carapace was prepared as usual while small amounts of algae and unidentified material were scraped from the surface of the other half. These scrapings were found to have a specific activity more than ten times that of the carapace as a whole (150,000 d/m/g compared with 14,000 d/m/g). When the small proportion of the total weight of the carapace represented by the surface material is considered, it is clear that little if any of the radioactivity was actually deposited in the exoskeleton. A similar situation was found with clam shell, where material scraped from the surface had a specific activity 68 times that of a portion of the shell taken as a whole (6800 d/m/g compared to 100 d/fm/g). In this case the surface material makegup an even smaller proportion of the total weight than it does in the crab carapace. Contemination of the skin of a species of sea cucumber, H. atra, is evident from a comparison with a second species, Stichopus sp., collected at Aarsanbiru (Table 19). A total of nine specimens was collected in four to seven feet of water within an area of less than one thousand square feet. The two species live side by side and are both detritus feeders. H. atra, however, has a habit of coating itself with sand while - 101 - meganteres eee eeeree eet in the skin and gut of the sea cucumber, and on the outer sur-