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BULLETIN OF THE UNITED STATES EISH COMMISSION. 
bears much resemblance to one of the longitudinal folds in the head-sheath of such 
species as Rattulus capucinus Wierz. & Zach. and Rattulus multicrinis Kellieott (pi. vi, 
figs. 58 and 59); and these folds are cross-striated, just as in the case of the furrow. 
The striations in the folds of the head-sheath are evidently line muscular bands, 
which have the office of bringing the folds together when the head is withdrawn. 
In the case of the dorsal striated area, it seems beyond question that the stria- 
tions are of the same nature — that they are muscular bands. They are clearly not 
surface markings, but are internal bands. This is seen with especial ease in such 
forms as Rattulus carinatus Lamarck and Rattulus bicristatus Gosse, in which the 
striated area rises in the form of one or two ridges. Moreover, the two edges of 
the furrow may be closely approximated, when the animal is strongly retracted, as 
in pi. VIII, fig. 70. When the head is extended the bases of the two teeth (on the 
opposite sides of the furrow) are a considerable distance apart; but when the 
animal is contracted to a maximum degree the two are almost in contact. 
The striated area therefore represents a longitudinal flexible portion of the 
lorica, permitting an increase or decrease in the circumference of the body. The 
striations are muscle fibers, bj 7 means of which the approximation of the two sides is 
brought about. These fibers are attached at the middle and at the two thickened 
edges of the area. 
In Rattulus mucosus Stokes (pi. x, fig. 86) the two edges of the striated area 
are raised as pronounced ridges, leaving a broad and deep furrow between them. 
The striations (muscle fibers) pass from the summit of the ridges to the bottom of 
the furrow. Stokes (1896) states that he has seen the two ridges drawn toward each 
other, and I believe that I have observed the same thing. 
In Rattulus bicristatus Gosse the two edges of the area reach their highest 
development, rising as two very high prominent ridges with a broad, deep furrow 
between them (pi. ix, figs. 77 and 78). The muscles are grouped in pronounced 
bundles, which p>ass from near the summit of the ridges to the middle of the broad 
groove between them. In a squarely side view of the ridges the ends of the muscle 
bundles are seen as irregular areas. 
In another series of species, of which Rattulus carinatus Lamarck (pi. xi, figs. 
95, 97), Rattulus lophoessus Gosse (figs. 98, 99), and DiureUa tigris Muller (fig. 1), 
may be taken as types, only the right edge of the striated area is elevated into a 
ridge, the left not rising above the general surface of the body. Thus a single ridge 
is x>roduced, having its edge toward the right, and sloping gradually to the left. 
The left edge of the striated area may usually be recognized as a sharp, well-defined 
line, but not at all elevated. The muscle fibers run from the summit of the ridge 
(on the right) to the base of the ridge, at the left boundary of the area. The inter- 
ruption of the fibers in the middle of the area can. usually still be made out (though 
it is not indicated in all the figures). 
Thus we have produced the peculiar condition found in many of the Rattulida 
and well shown in fig. 1 and fig. 95 (pi. xi) — a high, sharp) ridge passing on the 
right side of the body obliquely backward. Why the right ridge should thus have 
developed rather than the left one we shall try to bring out in our general discussion 
of the asymmetry of the Rattididce. 
In addition to the ly[>es already described the striated area is present, in a con- 
siderable number of s[iecies, neither in the form of a well-defined ridge nor as a 
