MARINE ISOPODA OF NEW ENGLAND, ETC. 299 



Underneatli, the mouth is seen to be protected by a pair of organs 

 called maxillipeds (pi. X, fig. 62 a), with which, for convenience of dissec- 

 tion, we shall commence the description of the parts of the mouth. The 

 five terminal segments of the maxillipeds in Girolana (numbered 1 to 5 in. 

 the figure) constitute the palpus, but this number varies in the different 

 genera. They are articulated to the external surface of the large basal 

 segment (w), usually proportionally much larger than in Girolana, as in 

 Idotea phosphorea (pi. V, fig. 2Sh,m), or in the "sow-bug" where the 

 palpus is greatly reduced. The basal segment of the maxilliped is, in gen- 

 eral, produced internally beyond the origin of the palpus, and furnished 

 with strongly plumose or pectinated setae at the tip. Frequently along 

 its inner margin one or more short styliform organs are attached, as in 

 Jcera alhifrons (pi. I, fig. 5), while along its basal margin is a more or 

 less distinct suture, indicating the epimeral segment of this organ, which 

 will be further explained. The basal segments of the opposite max- 

 illipeds meet along the median Hue, where their margins are nearly 

 straight, and to the base of the outer margin is attached a more or less 

 triangular external lamella (i)l. X, fig. G2 a, I). The name "maxilliped" 

 is frequently used for the basal segment only, which is often, as in the 

 " sow-bugs," much larger than the rest of the organ and serves to cover 

 and protect the other organs of the mouth. 



When the maxillipeds are removed we find two pairs of maxillae, the 

 outer and inner; of these the outer, or second pair (pi. X, fig. 61&), are 

 in general of a delicate texture, and three-lobed at the tip, the two 

 outer lobes being articulated to the basal piece, and all three lobes cili- 

 ated on their inner margins. The inner, or first pair of maxillae are of 

 a less delicate texture than the outer, and are hardly of the ordinary 

 form in Girolana (pi. X, fig. 61 c) ; reference may, therefore, be made to 

 Synidotea nodulosa (j)l. VI, fig. 35 c), where the two unequal lobes are 

 shown, the inner comparatively small, and supported on a slender pe- 

 duncle, curved inward, truncated at the tip, and bearing stout, curved^ 

 pectinated setae; the outer much more robust and larger, similar in 

 general outline to the inner, but armed with stout, curved, denticulated 

 spines at the tip. 



The mandibles (pi. X, fig. 61 d) are usually toothed at the apex, the 

 teeth being supported on a dentigerous lamella, which may be double 

 on one mandible, usually the left, and receive the lamella of the oppo- 

 site mandible between the two ; below this lamella is often a comb of 

 pectinate setae, and, generally, a molar process, as in Janira alta (pi. Ill, 

 fig. 12 &, m). In many genera a three-jointed palpus (pi. X, fig. 61 d, p) 

 is articulated to the external surface of the mandible, and, usually, the- 

 terminal segment of the palpus is more or less semicircular, or curved^ 

 and bears on its inner margin a very regular comb of setae (pi. Ill, fig. 

 12 b), apparently of service in cleansing the organs of the mouth. This 

 comb may be continued or repeated on the second segment, as in Giro- 

 lana (pi. X, fig. 61 d, p). In the " sow-bug" and many other genera the 



