166 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 
Expedition, described a new species of Arietellus under the above 
name, but his description and his two figures are very incomplete and 
really include only a single specific character, the long frontal spine. 
This, however, is enough to identify the species with the Albatross 
specimens, and the name given by Wolfenden must be retained. But 
there are many other distinctive characters shown by the various 
appendages, especially the fifth legs, which warrant a more complete 
description of both sexes. 
Female.—Body rather stout, head partially separated from the first 
segment by a dorsal groove; forehead produced into an elongated coni- 
cal spine one-fourth as long as the head and pointed straight forward. 
Thorax widest at the junction of the head and the first segment, second 
and third segments narrowed but little, fourth and fifth segments 
fused and produced at the posterior corners into broad acutely pointed 
spines, which extend backward to the second abdominal segment and 
curve upward at their tips. Urosome a fourth as long and a fourth 
as wide as the metasome, with the frontal spine and the caudal rami 
both included in the length. The fifth thoracic segment is visible in 
dorsal view in the posterior sinus of the metasome and gives the 
urosome an appearance of being 5-segmented. Genital segment wider 
than long and not protruding ventrally, with nearly straight sides. 
Abdomen 8-segmented, each segment wider than long, the anal seg- 
ment incised posteriorly. Caudal rami at the corners of the anal seg- 
ment and divergent, each a little longer than wide and with five 
stout setae. The three middle setae are much longer than the other 
two but are only normally plumose; the outer seta is at the middle of 
the outer margin. 
The first antennae are slender and reach just beyond the tips of the 
spines at the posterior corners of the metasome. ‘The endopod of the 
second antenna is a little longer than the exopod; the mandible palp 
is uniramose with the endopod entirely lacking. The first four pairs 
of legs are biramose, the rami 3-segmented; the fifth pair (pl. 3, fig. 
25) are uniramose and 3-segmented. Their basal segments are fused 
across the midline; the two plumose setae on the inner corners of the 
second segments and the appendicular filiform seta on the right leg 
are exceptionally long. ‘The third segments are nearly as long as the 
other two combined, slightly swollen at the base and tapered into long 
acuminate points. Total length 5.20 mm. 
Male——Body similar to that of the female but smaller, the anterior 
spine fully as large as in the other sex but the spines on the posterior 
corners of the metasome considerably smaller. The urosome is 5- 
segmented and the caudal rami and their armature of setae are pro- 
portionally larger and more densely plumose. The first antennae 
