^Eupanopeus herbstii^, ^Eurypanopeus depressus^, ^Neopanopeus texana^, ^Rhithropanopeus harrisii^ (Mary J. Rathbun). These four species, formerly all called /Panopeus/, are small crabs which live in the mud and are commonly known as mud-crabs. They are abundant under stones in muddy places, and occur on the Atlantic coast from Massachusetts Bay to Florida, though they are not commonly met with north of New Jersey. /Eupanopeus herbstii/ is the largest one of the group, some of the Southern ones measuring two inches across. It is found living in mud at low-water mark, or burrowing in banks near high-tide mark. It is dark olive-brown, the claws broadly tipped with black. /Eurypanopeus depressus/ is flattened above, and is smaller than /Neopanopeus texana/, which is somewhat convex above. The last two are commonly found together and have similar habits. /Rhithropanopeus harrisii/ lives near high-water mark and also in salt-marshes, and is comparatively rare. The claws lack the dark tips of /E. herbstii/, and a distinct groove follows the edge of the carapace. FAMILY ~GRAPSIDÆ~ GENUS ^Hemigrapsus^ ^H. nudus^ (Mary J. Rathbun), ^Heterograpsus nudus^ (Stimpson); ^H. oregonensis^ (Mary J. Rathbun), ^Heterograpsus oregonensis^ (Stimpson). These two species, commonly called respectively the /purple shore-crab/ and the /yellow shore-crab/, are the most abundant species of the California coast. Hundreds may be found congregated under a single rock. They range from Sitka to Lower California. /H. oregonensis/ literally swarms in sloughs of salt or brackish water, and hundreds of uplifted threatening claws confront the intruder who ventures on these mud-flats when the tide is out. This species, the yellow shore-crab, has a nearly square body. The anterior half of the side margins has two rather deep indentations, [pg282] making two spine-like projections which bend forward. The four posterior pairs of legs are more or less hairy; the chelæ are rather large in proportion. The male is about one inch across and the female is one third less in size. The general color is yellow. /H. nudus/ is found in the same localities, and differs from /H. oregonensis/ in being purple in color, with mottled claws, and in having the denticulations less pronounced and the walking-feet devoid of hairs. It is also a little larger. (Plate LXIII.) GENUS ^Pacygrapsus^ ^P. crassipes.^ A species very common on the California coast south of San Francisco. This crab is similar in general features to the purple and yellow ones described above, but is considerably larger, and the carapace is banded with color. FAMILY ~OCYPODIDÆ~ GENUS ^Ocypoda^