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muscle is very shallow and the adductor ridge is very feebly indicated; the cavity for the 
lateral depressor muscle is somewhat more distinct. 
The tergum (Pl. XXII, fig. 12, 6 and @) is short and rather broad. Its scutal margin 
is straight, its apex slightly, though not sharply pointed; its carinal margin is very feebly 
convex, and the two parts of the basal margin form together a straight line on opposite sides 
of the spur. Externally the tergum shows rather distinct growth-ridges and an open longitu- 
dinal furrow. The spur, which is obliquely truncated at the extremity, has a rather long free- 
extending part. Its width is about one fifth of the breadth of the entire valve. On the inner 
surface the articular ridge is long, but not very prominent, and the articular furrow is not very 
deep. The crests for the lateral depressor muscles are hardly visible. 
With regard to the structure of the animal’s body the following seems of interest: 
Mouth. Labrum (Pl. XXII, fig. 13) with shallow notch, wide at entrance and three 
teeth on each side of it; the sub-triangular portion is not very broad but rather elongate. 
The palpi are elongately oval, with the extremity rounded. The outer surface is furnished 
with a row of long and slender spine-like hairs standing at some distance from each other; 
near the free extremity the same surface is furnished moreover with a group of not very 
numerous hairs which pass imperceptably into the rather dense row of shorter hairs arranged 
along the upper margin. The hairs on the inner surface are short and delicate and grouped 
in the ordinary way: a longitudinal row is arranged in a line almost parallel to the upper 
margin and these hairs are directed towards the free edge of the labrum. 
Mandible (Pl. XXII, fig. 14). Distance of the extremities of teeth 1 and 2 greater 
than that between 2 and 3, in the proportion as 4 to 3. Teeth 1 and 2 pointed, 3 thick 
and indistinctly double. Tooth 4 is small, tooth 5 and inferior angle are represented by 
small nobs. 
Maxilla (Pl. XXII, fig. 15) with the edge straight, without a notch behind the upper 
pair of larger spines, and with five somewhat shorter spines on the middle part of the edge 
and two larger spines situated near the inferior angle, which itself bears a few shorter bristles. 
Several delicate hairs are observable between the spines. 
Outer maxillae have the outer lobe elongately oval, and over a large part (the 
outer half) of the inner surface densely clothed with hairs, rather numerous ones being arranged in 
a row over the inferior half of the same surface; the inner lobe has the interior face rounded 
and furnished with not very numerous, but rather long and feathered hair-like spines. 
Cirri. First pair with the rami very unequal, of 6 to 7 and 16 segments. Inferior 
segments with the inner faces somewhat protuberant. 
Second pair with short rami, of 5 and 6 segments; the inner faces rounded and not 
protuberant, densely clothed with brushes of spine-like hairs. 
Third pair considerably longer than cirri of second pair, having respectively 8 and 9 
segments in the two branches. Second to penultimate segments (Pl. XXII, fig. 16) of both 
rami having the rounded inner faces armed with numerous teeth, grouped in rows, and diminishing 
in size from the front margin (where they appear like strong downwardly-curved teeth), over 
the surface, to the posterior margin. 
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