Carapace considerably compressed and covered with minute granules and short hairs; cervical groove narrow, but distinct. Rostrum narrow and just reaches to tip of cornea, bordered with some sharp granules; its median ridge extended back onto anterior part of carapace; two rows of five or six spines at each side of median ridge; a short median ridge just at distal end of posterior margin of carapace. First two pereiopods chelate, the first being the much larger; both chelae with many bundles of stiff long setae and sparse spiniform tubercles. Abdomen smooth, and pleurae not sharp; tail-fan well developed, and some spines on dorsal surface of telson and longitudinal ridge of endopod of uropod.
Remarks:
In the collections at hand is a specimen referable to A. defensus Rathbun, 1901, but the state of preservation is not good for the photograph. The rostrum long and tapering suddenly, with a sharp supraorbital spine at each side; two teeth on crest from each supraorbital spine, and several small spines arranged in submedian longitudinal line.