The young of this species were very abundant at Laguna Beach, and I will give a short description of one because of the great variation from the adult. Plate II shows a young male with the antennæ inverted showing the setæ on the ventral side. The first five segments are of nearly equal length; peræon smooth; superior antennæ nearly half as long as the body, with inferior nearly as long as superior; flagellum with six to nine joints. Maxillipeds (Plate III, Fig. 5) with inner plate reaching apex of first joint of palp, armed with two teeth and spines; outer plate reaching apex of second joint of palp and armed with three small teeth. Upper lip (Fig. 6) bilobed, finely ciliated. First maxillæ (Fig. 7) two-jointed, palp and second joint armed with spines. Second maxillæ (Fig. 8) armed with a few hairs on the tip. Mandible (Fig. 9) has cutting plate made of five strong, unequal teeth; teeth of secondary plate nearly equal. First gnathopod attached far forward, triangular in shape and fringed with hairs. Second gnathopod (Fig. 11) attached the same as in adult, palm convex on inner margin, instead of concave as in adult, and armed with two small teeth near inner margin at the base; finger is concave and uniform in outline. _Caprella septentrionalis_ Kroyer The specimen here described differs slightly from those described by Mayer, Holmes, Sars and others, yet I do not think the differences great enough to demand the naming of a new species. The peræon (Plate IV, Fig. 12) is comparatively smooth, first two segments long, as long as the rest of the body; cephalon angularly produced in front into a very short, blunt spine. Figure 13 shows a specimen with a body somewhat broader. The superior antennæ are about half as long as the body, first joint broader than second, but shorter; second joint longest of all; third longer than first, and narrower than second; flagellum shorter than the peduncle and made up of about twelve joints. Inferior antennæ slightly shorter than the peduncle of the superior. Mandible (Fig. 14) cutting edge denticulate, with five irregular teeth, spine row having three large, feathery spines; molar tubercle strong and prominent. First gnathopod attached far forward, against the maxillipeds; hand triangular, fringed with hairs on the inner margin and one spine tooth near the base. Second gnathopod (Figs. 15, 16) attached near the posterior extremity of the second pereiod, basal joint nearly as long as the hand, inner margin of hand lying in a straight line and armed with two teeth near the base of the palm, one on the lobe and the other to one side. Another long tooth is near the base of the finger and is separated from a large, broad tooth by a deep suture; inner margin of the finger irregular. Third, fourth and fifth peræopods are similar in structure and not as stout as those of _C. geometrica_; hands powerful and armed with three clumps of spines on small prominences; differing in this respect from those described by