532 BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



STEGOPHRYXUS HYPTIUS Thompson. 



Stegophry.ms hyptius THOMPSON, Bull. U. S. Fish Comm., XXI, 1902, pp. 53-56, 

 pis. ix, x. RICHARDSON, Proc. U. S. Nat. Mus., XXVII, 1904, p. 59. 



Localities. Great Harbor, Woods Hole; Hadley Harbor, Naushon; 

 Edgartown and Warwick, Rhode Island, on Pagurus longicarpus. 



Description of adult female. " Broad in proportion to length, mar- 

 supiurn very large; abdomen about half the length of thorax, distinct 

 from it, six-jointed, with five pairs of triramous pleopoda and a pair of 

 oval uropoda. Length about 9.1 mm. Color yellowish-white, opaque. 

 Ovaries^ when full of ripe eggs, orange-yellow. 



" Head, from the dorsal side appears as an oblong elevation, ending 

 anteriorly in a blunt lobe, which represents the median portion of the 

 much-reduced front. As the lateral portions of the front are almost 

 wholly obsolete, appearing only as two inconspicuous lobes, the greater 

 part of the antennules, antennae, and tip of rostrum is visible dorsalty. 

 The antennules are three-jointed and consist of a large globose basal 

 joint, surmounted by a small cylindrical second and a minute third 

 joint; outer joints bristle-tipped. Each antenna arises along the side 

 of rostrum as a columnar ridge whose distal end is visible dorsally. 

 From this ridge a four-jointed flagellum arises, its proximal joint 

 stout, the three distal joints slender; all the joints bristle-tipped. 

 Ventral surface of head broader than dorsal surface and sharply ele- 

 vated at posterior border, giving a strong antero-dorsal slope, so that 

 the erect hypopharynx points almost anteriorly. At sides of poste- 

 rior border three curved processes arise, and in the midline are two 

 thin foliaceous plates. Rostrum conical. Mandibles slender, with 

 expanded tips, the edges of which are incurved so that pressed together 

 they form a sucking tube. Near the bases of mandibles appear the 

 oval maxillulae. Hypopharynx erect, highly keeled, and plays no part 

 in formation of rostrum. Maxillipeds large; each consists of a foli- 

 aceous anterior and a somewhat thicker posterior blade; during life 

 these organs keep up a rapid fanning motion. There is no trace of a 

 palpus. 



"The thorax is concealed ventrally by an enormous marsupiurn, 

 built up of five pairs of thin brood-plates, each strengthened by a 

 median chitinous rod. The posterior or fifth pair lie externally to the 

 others and form the major part of marsupium; they are attached 

 along the border of fifth and sixth thoracic segments. The posterior 

 angle of each forms a shallow pouch. Nearly concealed by these 

 plates, and almost closing the marsupium anteriorty, are the third and 

 fourth pairs of plates, similar to each other in shape and having an 

 oral ventral and a rounded dorsal portion. This dorsal part conceals 

 the legs of the parasite. The second pair of plates are oblong and are 

 hidden under the others. The first pair consists of a rather oval ante- 

 rior and a triangular posterior blade. The latter is strengthened 



