MARINE ISOPODA OF NEW ENGLAND, ETC. 403 



PLATE XI, FIG. 70. 



The deep constrictions, by which the second thoracic segment is sepa- 

 rated from the first and third, serve to distinguish this species from the 

 allied forms on our coast, and the "flower" at the end of the pleon dis- 

 tinguishes it from other Isopoda. 



Body moniliform, with evident segments; head narrower than, and 

 about half as long as, the first thoracic segment, flattened and quadrate 

 above, with a groove behind a raised anterior border, wedge-shaped 

 below, deeply emarginate on each side of the projecting front above for 

 the bases of the antennulse 5 eyes lateral, not conspicuous, extending 

 behind the emarginations. Antennulse (pi. XI, fig. 70 ) with the first 

 segment large but longer than broad, flattened above ; second and third 

 segments cylindrical ; flagellum of twelve or more segments in adult 

 specimens, with the first segment short, second twice as long and the 

 longest segment of the flagellum, which tapers from the second segment 

 and bears on the distal end of each segment an imperfect whorl of hairs. 

 The antennae (pi. XI, fig. 70 b) slightly surpass the antennulse. They have 

 the first segment short; the second flattened on the inner side, where it 

 is usually in contact with its fellow of the opposite side, and excavated 

 on the outer side above to accommodate the basal segment of the anten- 

 nulse ; the third segment is short ; the fourth and fifth longer and cylin- 

 drical. The flagellum consists of about twelve segments, tapers from 

 the base, and is somewhat hairy. Both the antennae and anteunulse 

 are a little less developed and have one or two less segments in the 

 females. The maxillipeds (pi. XI, fig. 70 c) are elongated, with a short, 

 oval external lamella, and a two-jointed palpus. The large basal seg- 

 ment of the maxilliped projects on the inner side nearly to the end of 

 the first segment of the palpus. The palpus has its segments of about 

 equal length and provided with a few scattered bristles. The inner 

 maxilla3 (pi. XI, figs. 70 d and d') are evident at the tip in an under 

 view of the head ; they are elongate and acicular, and minutely and 

 sharply retro-serrate toward the tip. The three-jointed palpus of the 

 mandibles is also conspicuous below; all three of its segments are 

 short, and the last, which lies ordinarily between the bases of the an- 

 tennae, is flattened, oval, and provided with the usual comb of seta3. 



The thorax is somewhat flattened above, cariiiate anteriorly below, 

 and has the last segment much the shortest. The first segment is wider 

 than the head and about twice its length, and is more closely united 

 with it than are any of the thoracic segments with each other; it is 

 strongly carinate below, especially on its anterior part, where the carina 

 ends in a prominent tubercle ; a much more slender carina bounds the 

 flattened dorsal portion laterally. The second segment is separated 

 from the first by a deep constriction, and is articulated so as to allow 

 considerable motion, especially in a vertical plane; its antero-lateral 

 angles are prominent in the form of low, rounded tubercles, and be- 



