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dark-purple; the teeth along that margin are sharp and prominent in the lower half. The articular 
ridge is only slightly developed, it does not terminate abruptly downwards, but it merges 
insensibly into the tergal margin. At the place of the adductor ridge, a longitudinal crest 
which is slightly prominent is observable, but this can be traced from the apex down to the 
basal margin of the valve. The cavities for the musculi depressores are only faintly indicated. 
The tergum (Pl. XXIV, fig. 12, 6 and @) is elongate and slightly beaked, the spur 
is truncated, obliquely cut off, its width not quite one-fourth of width of valve. The outer 
surface has a well-developed longitudinal furrow, which is narrow at the apex of the valve and 
increases in width towards the extremity of the spur. Growth-ridges distinctly developed, narrow 
and numerous. On the inner surface the articular ridge is well-developed, while the crests for the 
musculi depressores can hardly be made out. The same dark-purple that is seen along the 
upper part of the occludent margin of the scutum, is observable also along the inner side 
of the articular ridge, and along the carinal margin of the tergum. 
The study of the structure of the animal’s body yielded the following results: 
Mouth. Labrum with the notch not very deep, wide at entrance. Three small teeth 
on each side of notch. Shape of rhombiform shield-like portion much as in the other species. 
Palpi somewhat square, not strongly swollen towards the extremity, hairs less numerous 
than in A. glans, but the general arrangement is the same. 
The mandible (Pl. XXIV, fig. 13) has five teeth, and the lower angle truncated. 
The free edge is rather elongate, the lower part narrow. The second and third teeth are: 
double, the free margin of the fourth is dentated, the fifth is short and pointed at the extremity. 
The truncated lower angle bears two short spines. 
The maxilla has the upper and lower margins almost parallel — it does not in 
consequence grow much broader towards the free edge. This edge is nearly straight and 
the notch under the upper pair of larger spines is hardly to be distinguished. A double row 
of five spines, all of about the same length, is arranged between the upper and under pair 
of spines. ‘ 
The outer. maxillae (Pl. XXIV, fig. 14) have the outer lobe short, much shorter 
than in the other species of Acasfa I was able to compare; the inner lobe seems to be 
somewhat more elongate than is the case in the other species. The hairs are distributed over 
the inner surface of the lobes in the same way as in the other species; those observed on 
the line extending from the outer to the inner lobe do not form a regular double row, and 
those on the inner lobe are less numerous than in A. glans on the same part. 
Cirri. First cirrus has very unequal rami of 6 to 7 and 16 segments in an older 
specimen, and of 5 and 13 segments in a younger one. Those of the shorter ramus are somewhat 
broader, yet not protuberant on the inner face. Most segments of the longer ramus are of 
an almost quadrate shape. Spine-like hairs on the inner face of the segments of the shorter 
ramus, numerous ones at the extremity of the last segment of that ramus, but a few only 
at the tip of the last segment of the longer ramus. 
Second cirrus also with strongly unequal rami of 6 and g segments in a younger 
specimen and 6 and 7 segments in an older one. The segments are a little longer than broad ; 
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