Limulus polyphermis is an estuarine species ranging from Maine to Yucatan. Within the Gulf of Mexico large populations are found only along the coasts of Florida, Yucatan, and Campeche, i.e., only along the “entrances” to the gulf. It is a bottom feeder, burrowing into the substrate for clams and other invertebrates or scavenging over the bottom. Specimens have been dredged during all seasons of the year, throughout most of the range of the species, from “mud” and sand bottoms at depths up to 12.5 fathoms in water ranging from 12.5° C to 28.5° C and from 11 to 30.6‰ in salinity. In the northern part of its range Limulus apparently remains buried in the bottom most of the winter. Large concentrations of adult limuli and the immature stages and their exuviae are common in many estuaries of the United States. The adults migrate shoreward during the spring and summer, spawning at high tide along the beaches. The large numbers of mating animals reported by Cook (1857) have been much reduced by the extensive fishing of these animals for fertilizer. Concentrations of larvae are found in the nests on the beaches (Battey, 1883); young limuli on intertidal flats (Townes, 1938). The exuviae sometimes collect by the thousands, even millions, in the beach wrack during the summer. Supposing that similar large concentrations of the adults, young, and exuviae occurred in past ages, it is interesting to note that the extinct Limulidae are apparently only well represented in the lithographic limestone of the...