CUMACEA AND PHYLLOCARIDA—CALMAN. 7 
is no antennal notch and the anterior part of the lower margin of the carapace is pectinate. 
The ocular lobe is minute, without trace of an eye. 
The pleural plates of the second free thoracic somite are small and rounded. 
The postero-lateral angles of the fifth somite are rounded: 
The abdomen, including the telson, is longer by about one-fourth than the cephalo- 
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thoracic region. The somites have a dorsal median ridge and paired dorso-lateral and 
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ventro-lateral as well as some less marked transverse ridges. 
The telson is a little more than twice as long as the last somite, the post-anal 
portion occupying more than one-third of its length. The basal portion has a flattened 
dorsal surface with dentate lateral margins. The narrower post-anal portion bears 
five or six pairs of rather long lateral spines. 
The antennules have the last segment of the peduncle slender and twice as long 
as the preceding. 
The third maxillipeds have the basis hardly widened distally, its distal outer 
corner slightly produced, the merus narrower than the ischium, and with two strong 
teeth on its ventral surface distally. 
The first legs have the basis shorter than the distal segments together, the last 
three segments slender, successively increasing in length. The second legs have the 
‘arpus longer by about one-third than the two distal segments together. The posterior 
legs are stout. The third and fourth have each a minute exopod of two segments. 
The peduncle of the uropods is a little longer than the telson, with rather slender 
spines on inner side. The endopod is longer than the exopod, with eight to twelve 
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spines on inner edge, the first seement nearly as long as the second and third together. 
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Remarks.—According to the very artificial system of classification adopted by 
Stebbing in his revision of the Cumacea (Das Tierreich, 1913), this species would probably 
be placed in the genus Adiastylis, since the post-anal portion, being less than half of 
the total length of the telson, can hardly be termed “long.” Of the species brought 
together in that genus the only one having any special resemblance to D. Mawsoni is 
A costatus (Bonnier), which has oblique ridges on the carapace. It differs, however, 
in the arrangement of these ridges, in the absence of exopods on the third and fourth 
legs, and in a number of other characters. A close resemblance to D. Mawsoni can be 
traced within the restricted genus Diastylis (as used by Stebbing) in the group of species 
distinguished by the presence of vestigial exopods on the third and fourth legs of the 
female. This group includes five species, three of which are from the Alaskan area 
of the North Pacific, and the others from South Georgia and the Straits of Magellan. 
Two of the Alaskan species, D. Dalli and D. bidentata, resemble D. Mawsoni further 
in the general pattern of the obliquely ridged carapace. In view of the well-known 
affinity of certain elements of the North Pacific fauna with that of the sub-antarctic 
