234 
Three specimens belonging to the above species were obtained from the plankton collected 
at the following two stations. 
Stat. 128 (HENSEN vertical net, 700 metres to surface), 2 specimens. — Stat. 148 (HENSEN 
vertical net, 1000 metres to surface), I specimen. 
Aegisthus aculeatus is much smaller than the next species and the rostrum is not nearly 
so prominent. The antennules are seven-jointed. The knob on the upper margin of the first 
joint is comparatively short. 
This species has only been recorded from the Atlantic and Pacific Oceans. 
2. Aegisthus mucronatus Giesbrecht. 
Aegisthus mucronatus Giesbrecht, 1891, p. 476. 
Aegusthus mucronatus Giesbrecht, 1893, p. 573, pls. 46 & 49. 
Aegisthus longirostris T. Scott, 1893, p. 104, pl. XI, figs. 31—34. 
Aegisthus mucronatus | C. Thompson, 1903, p. 33. 
Aegisthus mucronatus Cleve, 1904, p. 185. 
Aegisthus mucronatus Farran, 1905, p. 46. 
Aegisthus mucronatus Pearson, 1906, p. 36. 
Aegisthus mucronatus Farran, 1908, p. QI. 
Aegisthus mucronatus van Breemen, 1908, p. 183, fig. 197. 
Twenty specimens of this species were obtained from the plankton collected at the 
following stations. 
Stat. 109. — Stat. 112. — Stat. 118 (HENSEN vertical net, 900 metres to surface). — Stat. 
128 (HENSEN vertical net, 700 metres to surface). — Stat. 138. — Stat. 141 (HENSEN vertical 
net, 1500 metres to surface). — Stat. 143 (HENSEN vertical net, 1000 metres to surface). — 
Stat. 144. — Stat. 148 (HENSEN vertical net, 1000 metres to surface). — Stat. 203 (HENSEN 
vertical net, 1500 metres to surface). — Stat. 215", — Stat. 216. — Stat. 276 (HENSEN 
vertical net, 750 metres to surface). 
This is a moderately large species with six-jointed antennules. The knob on the distal 
end of the upper margin of the first joint is very prominent. The rostrum is long and pointed. 
Aegisthus mucronatus appears to have a wider distribution than the previous species. 
It has been recorded from the Atlantic Ocean, off the Coast of Africa and off the West Coast 
of Ireland, and from the Pacific. The form described by my father from the Gulf of Guinea 
as degisthus longirostris appears to be identical with Aegzsthus mucronatus Giesbrecht. 
40. Family Monsrriviipae. 
Genus Monstrilla Dana, 1848. 
The body is elongate and rather cylindrical. The cephalic segment is of considerable 
size and in some cases exceeds the combined length of the thorax and abdomen. There is no 
true rostrum. The abdomen is composed of three segments in the female and four in the 
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