MARINE ISOPODA OF NEW ENGLAND, ETC. 397 



This family is represented within our limits by three species belong- 

 ing to as many genera, which, in addition to the characters given above, 

 agree fiu'ther in the following particulars: The body is elongated and 

 vermiform, often more than ten times as long as broad, and of nearly 

 uniform size throughout. The head and thoracic segments are all dis- 

 tinctly separated from each other, and the head and last thoracic seg- 

 ment are shorter than the intervening segments, which are subequal. 

 Both pairs of antennae are approximate at their bases, and the lower pair 

 or true antennte are short, not greatly surpassing the head in length. 

 These organs have the basal segment short, the second segment flat- 

 tened internally and adapted to its fellow of the opposite side, while 

 above and externally it is excavated for the basal segment of the anten- 

 nulaB. The mandibles are palpigerous, and the mouth parts are titted 

 for piercing and for suction. 



In the first pair of legs the first, second, and penultimate segments are 

 enlarged and thickened; the two intervening segments, merus and car- 

 pus, are short ; the dactylus forms a curved finger tipped with a stout 

 spine and capable of complete flexion on the robust propodus. In one 

 or two of the succeeding pairs of legs the propodus may be slightly en- 

 larged. The first three pairs of legs have the carpus, or antepenulti- 

 mate segment, triangular, and their basal segments are directed strongly 

 backward. In the last four pairs the carpus may be short, but is not 

 triangular, and always distinctly separates the merus from the propodus ; 

 they are so articulated to the body that their basal segments are directed 

 forward. The first three pairs of legs are articulated to the anterior x)art 

 of the segment to which they belong, the next three near the middle of 

 the corresponding segments, and the last pair near the i30sterior margin 

 of the last segment. 



The pleon is short, with the segments more or less consolidated, and the 

 pleopods are of the normal number and form. The " operculum" is not 

 formed as in the Idoteidce and Arctiiridce of the lu^opods, but is nothing 

 more than the enlarged and thickened first pair of pleopods, the greater 

 part of it being formed of the external lamella, while the uropods have an 

 entirely difi'erent and peculiar structure. They are biramous, and con- 

 sist on each side of a more or less elongated, flattened, basal segment, 

 so articulated as to lie alongside the telson, and bearing at the apex a 

 terminal plate, the inner ramus, in the same x)lane with itself, while, on 

 its upper side near the base, stands a more or less perpendicular, oval 

 plate, the outer ramus. The telson is directed obliquely downward, and, 

 with the uropods, forms a ciliated cui^-hke or flower-like termination of 

 the cylindrical body, whence the name AntMra, from the Greek u'^&og, 

 a flower, and oupd, a tail. 



The structure of the mouth in tkis family has been investigated by 

 Prof. J. 0. Schiodte, to whose original papers in the Naturhistorisk 

 Tidsskrift I have not had access. The paper on Antliura is translated 

 and partly condensed in the Annals and Magazine of Natural History, 



