828 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
24. Ttattulus longiseta Schrank (pi. tiii, figs. 67-72). 
Synonyms: Bracliionus rattus Schrank (1793); Vaginaria longiseta Schrank (1802); Monocerca bicornis Ehrenberg 
(1830, 1838); Monocerca cornuta Eyferth (1878); Acanthodactylws bicornis Tessin (1886); Mastigocerca bicornis 
Hudson & Gosse (1889) . 
Distinguishing characters . — The characteristic features of this animal are the two long spines 
at the anterior dorsal edge of the lorica. Of these the right is much longer than the left. The 
only species which at all resembles this is Rattulus roseus Stenroos, which is said to have the spines 
at the ventral anterior margin instead of the dorsal (but see the account of that species, p. 341). 
External features . — The body is usually fusiform in shape; when well extended it is elongated, 
widest at about the middle or a little in front of the middle, and tapering thence regularly back- 
ward to the foot. But the form of the lorica varies greatly with the degree of extension of the 
animal, as well as with the age of the individual. Young specimens are often broadest near the 
anterior end (especially when the head is retracted, fig. 68) , and the body is slender and tapers 
rapidly to the foot. The lorica is flexible and permits great changes of form in one and the same 
individual. When strongly retracted the animal is shorter and thicker, and the body becomes 
almost oval in form (fig. 70). The anterior portion of the lorica or liead-sheath is not distinctly 
marked off from the rest in this species, though a notch at the point of separation can usually be 
detected on the ventral side when the animal is retracted (fig. 70). 
The lorica is marked on the dorsal surface a little to the right of the middle line by a shallow 
longitudinal furrow, passing backward from the anterior end to about the middle of the length of 
the body (fig. 67). The direction of the furrow is slightly oblique, its anterior end lying a trifle 
farther to the right than its posterior end. The furrow is marked by transverse striations, really 
muscle fibers, attached within the two ridges which form the boundaries of the furrow. These 
two bounding ridges project at the anterior margin of the lorica as two long spines, forming the 
most characteristic feature of this animal. The right one of the two spines is the longer, usually 
twice as long or more than twice as long as the left. (Weber, 1898, figures the left spine as the 
longer, and Gosse, 1855, states that the left spine is the longer in this species. It is, of course, pos- 
sible that there is variation in this matter, but I examined a large number of preserved specimens 
with this matter in mind, and found that in all cases the right spine was longer.) 
The head-sheath has longitudinal plaits or flu tings, where folding takes place when the head 
is retracted. The anterior margin of the lorica differs exceedingly in the contracted and expanded 
conditions. In a fully extended living individual (fig. 67), the anterior part of the lorica is wide 
open, and the margin shows, in addition to the two long dorsal teeth, four or more minute points, 
lateral and ventral. There is usually no trace of the longitudinal folds so prominent in the 
retracted individual. In retracted specimens (figs. 68, 70), on the other hand, the anterior opening 
is much smaller, and many ridges and grooves are visible, owing to the folding of the lorica. Each 
of the longitudinal ridges runs out to form a small point or tooth, so that the anterior margin 
seems to bear many teeth. 
Corona . — The corona bears a large dorsal frontal process; otherwise it has not been thoroughly 
studied. 
Antennae . — The dorsal antenna lies within the striated furrow, a short distance from the 
anterior end (fig. 67). The two lateral antennae are in the usual position, one on each side, about 
one-fourth the body length in front of the foot. In specimens where an exact comparison between 
the two was iwssible, the left antenna was situated a little anterior to the right. 
Foot . — The foot is a short, conical structure, attached to the body only slightly obliquely, so 
that its movement is not so nearly limited to a turning to the right as we find it to be in many of 
the Rattulidce. 
Toes . — The right toe (fig. 69, r. t.) has nearly disappeared, so that it is customary to speak of 
the left one as the toe. while the right is classed merely with the substyles. The main toe is 
usually about two-thirds the length of the body. The substyles are small scales, one of which lies 
on each side of the main toe and the rudimentary right toe. The latter lies a little above the main 
toe, with its tip against it. 
Interna 1 organs . — The eye is attached to the brain, and in a dorsal view lies usually consider- 
ably to the left of the dorsal furrow on the lorica. The trophi (figs. 71 and 72) are unsymmetrical, 
the right malleus being much more slender than the left. (For a full description of the trophi in 
this species see the general account of the trophi, p. 289.) 
