[There is no abstract or summary for this work; the following passage on p. 406 is offered in HTML format as an example of content. Editor March 2009] Many of the species of the genus Arcturus are very similar in bodily contour and armature; the various appendages appear to afford the best characters whereby the species may be distinguished, and in this respect full use has been made of the relative length of the body segments, joints of the antennae, and of the legs. A glance at the text and the accompanying figures will serve to show the value of the variation in the comparative length of joints of the larger limbs.
The position, number and character of the denticles or spines are also of importance. In some species the armature consists of a series of serrations; in others, of distinct spines, generally fixed, but occasionally mobile, especially near the extremities.