312 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
6. Diurella porcellus Gosse (pi. n, figs. 19-23). 
Synonyms: Diurella. tigris Bory de St. Vincent (1824); Monocerca porcellus Gosse (1851); Acantliodactylus tigris 
Tessin (1886); Ccelopus porcellus Hudson & Gosse (1889). 
Distinctive characters.— This species is to be known by the short, plump, curved body; by the 
two toes, one a little longer than the other, usually kept folded beneath the body, and especially 
by the two teeth at the anterior margin of the lorica on the dorsal side. From all the other 
closely related species it differs in the presence of these two teeth, the others having one or none. 
External features . — The body is short and thick, and strongly curved, so that the back forms 
an arc of a rather small circle. The posterior end is broad and rounded, the opening for the foot 
being on the ventral surface. The head-sheath is marked off from the remainder of the lorica by a 
slight constriction; it bears at its anterior margin, a little to the right of the middle line, two teeth, 
which are very similar to those of Diurella insignis Herrick. The right one of these is the longer, 
and is separated from the left by a slight interval. Ventrally the anterior margin has a broad, 
shallow notch. When the lorica is strongly contracted the two sides of this notch project as two 
decided points, one of which is seen in fig. 20. These two points might be called teeth, and this 
animal is therefore sometimes said to have four anterior teeth, two dorsal and two ventral. These 
two ventral teeth, due to the folding of the liead-sheath, are of a different character from the dorsal 
ones, however, and are not to be noticed when the head is fully extended. 
Extending backward from the larger one of the two dorsal teeth is a ridge, having its edge 
directed to the right. It is striated transversely from near its summit to a line some distance to the 
eft of it. The ridge is not prominent, and in some specimens there is a decided depression just to 
the left of the ridge, so that the ridge appears merely as the edge of the depression. In other cases 
the back seems nearly smooth, only the striated area being visible, with perhaps a marked line 
at its right edge. These differences are probably functional changes due to the varying states of 
contraction of the specimens, though I have not been able to demonstrate this. 
Corona . — The corona has a short, median, club-shaped process. It has not been fully studied 
in other respects. 
Antennce.— The dorsal antenna is just to the left of the ridge, in the depressed area, when the 
depression is present. It is situated a little behind the constriction which sets off the head-sheath. 
The lateral antennae are in the usual position- on the posterior one-fourth of the body, the left one 
somewhat in advance of the right. 
Foot . — The foot is very small and partly inclosed within the lorica. 
Toes . — There are two unequal toes, the left one being about equal in length to the diameter of 
the body, while the right one is a little shorter (fig. 23). Each of the toes is accompanied at its 
base by two substyles, one of them in each case being more than half the length of the shorter toe. 
The right toe usually lies with its tip against or across the longer left toe. This gives an appear- 
ance which Gosse (1889) interpreted as being due to two flat, spoon-shaped toes, the one lying 
within the other. The inner sides of the two toes were supposed to be the outlines of the smaller 
toe; the outer sides those of the larger toe. On the basis of this supposed structure the genus 
Ccelopus was founded. 
Internal organs . — The trophi are unsymmetrical, though the right manubrium is not lacking, 
as represented by Gosse (1855). It is a very slender rod. a mere bristle, but of the same length as 
the left manubrium. The latter is markedly “crutch-shaped ” in side view (fig. 21), though this 
is not noticeable in a dorsal or ventral view. The remainder of the internal organs call for no 
special mention. 
Measurements. — Length of body without toes, 0.14 to 0.15 mm.; toes about 0.05 to 0.06 mm. 
History. — This species was first described by Bory de St. Vincent in 1824, as Diurella tigris. 
Since the name tigris had been given by Muller to another species, Bory’s name can not be 
retained for this species. It has been used, however, by many investigators since Bory’s time. 
For a list of accounts of this animal under the specific name tigris , see the list given in the account 
of Diurella tigris Muller, above. Gosse (1851) described this animal as a new species, under the 
name Monocerca porcellus; this specific name porcellus is therefore the correct one to use, under 
the accepted rules of nomenclature. In Hudson & Gosse’s Monograph (1889) Gosse founded a 
new genus, Ccelopus, for this and a number of related species. As set forth in the general account 
of the taxonomy (p. 300) , this genus was founded on a mistaken idea and was without justification, 
