1886] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 321 



ventral coDcave anteriorly aud strougly convex i^osteiiorly, giving a 

 much greater depth to the head in the region of the mouth than at the 

 front, the greatest thickness being nearly equal to the greatest width. 



The thorax is short aud broad, not more than half as lung as, aud 

 somewhat narrower than the head. Viewed from above it presents two 

 rounded lobes on each side, produced by a constriction near the front ; 

 the anterior lobes merge into the head, the posterior are larger aud 

 better defined. 



The abdomen enlarges abruptly from the thorax and is very broad, 

 especially toward the front, its greatest width being nearly equal to its 

 length, or even exceeding it in specimens that are much contracted. 

 A slight, narrow constriction at the sides partly divides it into two seg- 

 ments, of which the anterior is slightly longer than the posterior iu 

 specimens in normal condition, bnt often very much larger iu the youug 

 or contracted ones. The greatest width of the body is across the an 

 terior segment, and its thickness at the same place is considerably more 

 than half the width, the median ventral surface being more or less 

 raised and the margins broadly thickened. The posterolateral prolon- 

 gations of the abdomen are large aud stout, rounded at the ends, and 

 generally extend obliquely downwards and backwards, though some- 

 times nearly at right angles to the rest of the abdomen. 



The genital segment is relatively small, the tail nearly as large, globu- 

 lar, and reaching back nearly as far as the hinder prolongations of the 

 abdomen; in young specimens it projects back of the latter. The ovig- 

 erous tubes are of nearly uniform size throughout, or taper slightly. 



The anterior antenuse are very small, slender, rounded, two jointed, 

 aud do not reach quite to the sides of the front margin ; they originate 

 at the extreme end of the ventral surface of the head, very near the 

 median line. The basal joint is elongate, aud slightly constricted at 

 the inner end; the terminal joint is short, about one-third as long as, 

 and narrower than, the tasal, and is rouuded at the outer end, where it 

 is armed with several small elongate papillie; there is also one similar 

 papilla near the middle of the posterior margin. The posterior au- 

 tennse or prehensile hooks are rather large; the principal joint stout, 

 strongly curved throughout, and sharply pointed; the basal short and 

 broad. The mouth parts do not differ greatly from those of G. galeritiis; 

 the three principal pairs of organs are represented on plate X, figs. 10-12. 



The thoracic appendages are of moderate size, relatively stout, aud 

 notched or slightly bilobed at the ends; those of the anterior pair are 

 not much more than half as long as the posterior, the latter reaching to 

 about the middle of the first abdominal segment. The anterior ]>air 

 originate close to the head, and in side view appear subcircular or sub- 

 ovate in section, while the posterior are oblong or short clavate, and 

 about twice as long as broad. The former are but slightly indented at 

 the ends, each terminating in two rounded knobs, the outer somewhat 

 larger than the inner, and often presenting, when viewed from the ends, 



