326 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
extended this hook is frequently not visible: it seems to be either turned back or hidden by the 
cilia. Such a case is shown in fig. 63. This fact, if not carefully noted, is likely to lead to incor- 
rect determinations of specimens not showing the hook. There is a slight furrow passing back 
from the base of the hook in the dorsal median line for about one-third the length of the lorica, 
and this furrow is marked with faint cross-striations. We have in this species, therefore, a slightly 
marked “ striated area,” which seems to be quite lacking in its nearest relatives, R. multicrinis 
Kellicott and R. capucinus Wierz. & Zacli. 
Corona. — The corona has not been studied thoroughly. The preserved specimens at my 
disposal did not permit of such study. There are two slender, lateral, antenna-like appendages, 
however, as seen in fig. 63. 
Antenna:. — The dorsal antenna is long and usually very prominent, as shown in figs. 62 and 
63. In other cases it is merely a bundle of short, hair-like processes (fig. 64), while in still other 
preserved specimens I have not been able to see it at all. In these cases the antenna may have 
been injured. 
Lauterborn (1893) described this species as new under the name Mastigocerca set if era, 
merely because Imhof (1891) did not mention the dorsal antenna in his original description. 
Lauterborn held that owing to the prominence of the dorsal antenna it could not have been over- 
looked if Imhof had really had this species before him. This is negatived by the fact, just stated, 
that specimens are often met with in which the antenna is inconspicuous or invisible. Minkiewicz 
(1900) described this same species anew — again without mention of the dorsal antenna — though 
specimens of his species, received through his courtesy, show the prominent antenna clearly. It 
is thus evident that because the antenna is not mentioned in a description one can not conclude 
that it is nonexistent nor even that it is inconspicuous. The name Mastigocerca set if era has there- 
fore no foundation and must be considered a synonym of R. cylijndrjfcus Imhof . a 
The lateral antennae, as Bilfinger (1894) has shown, are strikingly unsymmetrical in position. 
The left is on the flank, at about the middle of the length of the lorica (fig. 63), while the right is 
far back, almost exactly at the junction between the lorica and foot. 
Foot. — The foot is very small, and not clearly marked off from the rest of the body. 
Toes. — In this species the disproportion between the right and left toes has reached its maximum . 
The right is a mere, minute, scale-like bristle, hardly noticeable, while the left (forming the “ toe 
proper”) is a long, straight rod, almost or quite as long as the entire body of the animal. There 
is a small substyle on the outer side of the main toe, nearly as long as the rudimentary right toe 
(fig. 64). The latter lies, as usual, across the base of the main toe. 
Internal organs . — The eye is situated at about the middle, or a little behind the middle, of the 
long brain (fig. 64). The trophi have not been thoroughly studied. The specimens which I have 
had at hand have not shown these clearly. According to Bilfinger (1894), they are nearly sym- 
metrical. The ovary (fig. 64, ov.) may be seen to be connected behind with the cloaca. The egg 
is carried in this species attached to the posterior part of the lorica, above the foot (fig. 62). No 
other species of the Rattulidce is known which thus carries the egg with it. The other internal 
organs call for no special remark. 
Measurements. — Length of body, 0.26 mm. to 0.31 mm. : of toe, 0.23 mm. to 0.32 mm. ; total, 0.49 
mm. to 0.63 mm. 
History. — This species was described briefly, without a figure, by Imhpf (1891). In 1893 Lau- 
terborn redescribed it, at first identifying it with Imliof's species, but in a postscript to his paper 
giving it a new name ( Mastigocerca . set if era) , because Imhof had failed to mention the prominent 
dorsal antenna. (See the account of the dorsal antenna above.) The first figure of this species 
was given by Bilfinger (1894), together with a good description. Zacharias (1897) redescribed the 
animal under the name Mastigocerca, hamgta. The specimen figured by Zacharias shows a more 
slender form than any of the other figures given, and the body slopes even more gradually to the 
foot than in my fig. 64. But as these points are clearly very variable (compare fig. 62 and fig. 64) , 
and Zacharias's specimens agreed in other points with this strikingly characterized form, especially 
in the hook and the very long toe, it seems beyond doubt that his species is the same as R. 
" If this were not done, we should be forced to the absurdity of identifying as R. cylindricus those specimens in 
which for any reason we could not see the antenna, while others would receive the name R. setifer. 
