EUCHLANID. 89 
To get a clear notion of the form of the lorica,’ suppose that the shell of a tortoise 
has its flat base split longitudinally down the middle ; and then that half of each part, 
on either side of the split, is bent down at right-angles to the flat base. Further suppose 
that a second flat oval plate, smaller than the base, is cemented to the free edges of the 
bent-down parts, and the resulting form will closely resemble the lorica of an Huchlanis. 
It is obvious that a small box will thus be formed below the true base of the tortoise- 
shell, and that its cavity will be continuous with that of the shell, and that its bottom 
will project on either side as a flange. Moreover, on the outside of this box, on either 
side of it, will be a long furrow, bounded by the oval plate above, the flange below, and 
by the side of the box. In the actual lorica of Huchlanis the portion corresponding to 
the small box, below the true shell, contains a considerable portion of the viscera; while 
the furrow (when the animal is viewed sidewise) often presents the edges of the two 
bounding planes so as to look merely like two parallel lines running from front to 
rear. If we further suppose that the altered tortoise-shell, with its attached second plate, 
is made of glass, and that it is held up so as to have the lower plate fully exposed to 
view, it is clear that we shall see three sets of edges. First the outside edge of the proper 
base of the shell; secondly, within the first and parallel to it, the smaller oval edge of 
the lower attached plate; and thirdly, within this latter oval, the edges of the bent 
portions to which the lower oval plate is attached, and which connect the upper oval 
plate to the lower one. All these lines can be plainly seen in the ventral surface of 
H. dilatata (Pl. xxiii. fig. 5); where a is the edge of the dorsal plate, b is the edge 
of the ventral plate, and ¢ the edge of the connecting portion at right-angles to both. 
The position of the imner two of these three lines varies greatly with the different 
species, according to the relative sizes of the upper and lower flat plates; and so does 
the distance between these plates, and consequently the breadth of the longitudinal side 
furrows. These differences are great helps in distinguishing the species, which have 
been much confounded. Another assistance is the presence or absence of a sharp notch 
(Pl. xxii. fig. 2b) in the occipital dorsal surface of the lorica. In some species there is 
no such notch, but a wide gap (PI. xxiii. fig. 5a), and the dorsal portion of the lorica near 
the head is membranous ; so that it has no constant outline when the head is retracted. 
Mr. Gosse is of opinion that his two species, H. deflexa and EL. pyriformis, as well as 
a third lately discovered by him, have no ventral plate, but have a ventral membrane 
instead of it. On this account, as well as on account of a peculiarity in the structure of 
their rami, he would separate them from Huchlanis as a new genus, under the name 
Dapidia. As, however, we do not agree on the first of these two points, we have 
thought it better to leave the creatures, for the present, with their names unaltered. 
Ehrenberg has made use of delicate sete, which are sometimes found on the foot, 
in order to separate the species; but neither Mr. Gosse nor myself thinks this a cha- 
racter that can be trusted. For the sete are difficult to be seen, are liable to injury, 
and are certainly not constant in their presence in the same species. The internal 
structure of the various species is so closely alike that a description of it in one species 
will very nearly serve for that in any other. 
RK. tyra, Hudson, sp. nov. 
(Pl. XXIII. fig. 1.) 
SP. CH. Lorica long, narrow, oval, depressed ; transverse section a low circular 
segment ; dorsal occipital edge membranous; hind dorsal edge without a notch ; 
ventral plate with a very narrow flange, of wavy outline, elliptical and broadest at the 
hind end ; sete absent. 
' Ehrenberg quite misunderstood the lorica of Huchlanis, which he imagined to be open down the 
ventral surface between the two inner lines c,c¢ (pl. xxiii. fig. 5). This mistake, and the omission to 
draw or account for the line b, b, has led to endless confusion in determining the species. Dr. Cohn, 
however (in Sieb. wu. K6ll. Zeits. ix. 1858, p. 289), fully explained the error about the lines c,c; but 
missed the flange of the ventral plate with its edges 6, b. 
