ROTATORIA OF THE UNITED STATES. 
283 
well-defined groove, but merely as a flexible area with marked transverse striations. 
This is the case, for example, in Rattiilus rattus Muller (pi. xi, figs. 100, 101). In 
this organism the striated area is in some cases apparently swollen out to form a 
slight rounded ridge; in other cases it seems to lie at the general level of the lorica 
surface, while in still other specimens it seems to form a slight depression. It is 
probable that these are functional differences, due to the state of contraction or 
extension of the specimen. Almost every intergradation is found, from the furrow 
of R. elongatus Gosse to the high ridge of R. carinatus Lamarck. In perhaps the 
majority of species (especially in Diurella ) the striated area is merely slightly 
elevated at its right edge, forming a low ridge, not conspicuous in most views. 
The area in which the transverse striations can be seen usually passes from the 
anterior edge to the middle of the length of the body, or to a point some distance 
behind the middle. The ridge formed by the elevation of the area sometimes con- 
tinues back farther than the striations, and may extend to the beginning of the 
foot (as in Rattulus lophoessus Gosse, pi. xi, figs. 98, 99). 
Among the species which I have studied with care only Rattulus talus .Jennings 
and perhaps Rattulus multicrinis Kellicott and Rattulus capucinus Wierz. & Zach. 
show no sign of the striated area. 
A word further should be said about the relation of the striated area to the 
teeth or spines at the anterior edge of the lorica. Those of the second category 
mentioned on page 280 are formed as outgrowths of the thickened edges of the 
striated area. Where two teeth are present both the edges project, that formed by 
the right edge being usually the longer. When only one tooth is present it is 
formed by a projection of the right edge of the area. 
The anterior projections of the first category mentioned on page 280, found 
only in Rattulus cylindricus Imhof, Rattulus capucinus Wierz. & Zach., and 
Rattulus multicrinis Kellicott, are formed in a somewhat different way. The 
initial stage in the production of such a projection is found in Rattulus elongatus 
Gosse (pi. xu, fig. 102); the entire width of the striated area projects at the anterior 
edge as a rounded lobe. In Rattulus capucinus Wierz. & Zach. and R. multi- 
crinis Kellicott the projection has developed into a large triangular tooth. In 
Rattulus cylindricus Imhof (pi. vn, fig. 62) the tip of this tooth has further developed 
into a long hook, curved down over the corona. The three species showing this 
peculiar differentiation occupy a different position from most of the other species 
in many other respects also. 
(3) Foot. — The foot is a short., conical structure attached to the body at the 
posterior end. The foot shows little variation in structure, except in size and form, 
being in some cases short and thick, in others slender. In a few cases ( Diurella 
porcellus Gosse, D. sulcata Jennings, etc.), the foot is very small, so as to be hardly 
recognizable as a separate structure. In some of these cases it is usually held 
completely retracted within the body. Sometimes the foot shows one or two faint 
aim ulations which have at times been described as joints. 
The most peculiar thing about the foot in the Rattulidce is its usually un sym- 
metrical attachment to the body. The joint between the foot and the body is 
commonly oblique, extending farther back on the left (or left, dorsal) side than on 
the right. This is well shown in fig. 86 (pi. x), fig. 99 (pi. xi), and fig. 103 (pi. xll). 
In some cases the posterior edge of the lorica projects backward some distance over 
