54 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
thin brood-plates, each strengthened by a median chitinous rod. The posterior or fifth pair (fig. 4, 
Bp b ) 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 (fig. 
4, Po). Nearly concealed by these plates, and almost closing the marsupium anteriorly, are the third 
and fourth pairs of plates, similar to each other in shape (fig. 2, Bp s ) and having an oval ventral and 
a rounded dorsal portion (fig. 3, Dbp 3 and Dbp 4 ). This dorsal part conceals the legs of the parasite. 
The second pair of plates are oblong and are hidden under the others (fig. 2, Bp 2 ). The first pair 
consists of a rather oval anterior and a triangular posterior blade. The latter (fig. 2, Php x ) is strength- 
ened along its outer (longest) border and across its base by a chitinous rod. The anterior blades 
(fig. 2, Abpj), in company with the dorsal portions of the third pair of plates, form the funnel-like 
anterior end of the marsupium. 
The details of the thoracic segments are shown in fig. 3. The first five are crowded together, 
their fleshy lateral portions strongly bent toward the head. The lateral parts of first four segments 
end in a small roughened boss or cushion, on which the roughened third joint of the pereiopod 
impinges. This cushion ( C'u ) may represent a modified epimeron. Internally to this cushion is a flat 
shield-shaped area which comes in contact with the abdomen of the host (fig. 6, Sh). The lateral 
portions of fifth segment end in a sharp crest, and there is no “shield.” The sixth segment is very 
long; it narrows posteriorly, has a fleshy median keel and only slightly developed lateral portions. 
The seventh segment is short, fleshy, about as wide as sixth and similar to it except that it is not 
keeled. Ventral surface of thoracic segment fleshy, posterior borders of sixth and seventh modified 
into complex elevated keels (fig. 8). ( In the plate it will he noted that the first serrated keel belongs 
to segment 6, the second to segment 7, the third ( X ) to the first abdominal segment.) Pereiopoda of 
the sixth and seventh segments are alike and quite simple in construction (pi. 10, fig. 7); those of 
the other five segments are modified, the last three joints being twisted to one side (pi. 10, fig. 6). 
Extensor muscles enormously developed. 
The abdomen (pi. 9) consists of six fleshy segments, five of which bear a pair of pleopoda: Each 
pleopod has three oval blades arising from a short common hase. Two of these are subequal and 
extend in a lateral direction; the third is smaller and points ventrally. Tins ventral ramus is broadly 
expanded in the pleopoda of the first abdominal segment, especially on the right side (fig. 4, Vpl x ) . 
The first segment has ventral keels, similar to those on the last thoracic segments. Between the oval 
uropoda of the sixth segment ( Ur) is a minute conical prominence. 
Description of Adult Male. (Plate 10. ) 
Three and two-thirds longer than broad. Abdomen unsegmented, about a third of entire length. 
Color dull yellowish. Around the heart in the abdomen is an orange-colored area and a narrow streak 
of same color runs forward along the mid-dorsal line. Sometimes splashes of black occur on the sides 
of the head and thorax. Length about 3 mm. 
Head (pi. 10, figs. 1 and 2) oval, elevated in center, the margin entire and not inflexed. Eyes 
minute (fig. 1, E). On the under side is a shallow central depression, in front of which arise the 
short 3-jointed antennuhe (Aj). From the depression the 8-jointed antennae (A 2 ) and the conical 
rostrum take their origin. First joint of antennae elbowed, the others cylindrical, the distal ones 
bristle-tipped. Sixth, seventh, and eighth joints very small, together scarcely equaling the fifth in 
length. Rostrum prominent, built up dorsally by the lahrum ( La) and ventrally by the hypopharynx. 
Apex of latter conceals tips of mandibles and median part of labrum. Mandibles ( Mnd ) slender 
with thick bases and sharp chitinous tips. I have not found maxillulae. Between the maxillae, and 
extending forward from a transverse ridge, are the 3-jointed (?) maxillipeds ( Mxp ). The thorax 
consists of seven fleshy segments. It narrows slightly posteriorly and is moderately convex. Sides 
subparallel, somewhat deflexed, epimera not distinct. First segment notched for reception of head. 
Seven pairs of pereiopoda, whose structure and musculature can be understood by reference to the 
plate (pi. 10, fig. 8). Abdomen ovoid or sometimes pear-shaped, shows no signs of segmentation, and 
has no traces of appendages. 
Description of Immature Forms. 
I. The development of the youngest female specimen taken (pi. 10, figs. 9 and 10) was a little 
more advanced than the stage which Giard has called the “phryxoid” stage. It may he termed the 
metaphryxoid stage. More slender than adult; nearly three times longer than broad. Lateral 
portions of the thorax distinct from and scarcely wider than median part. Marsupium present but 
