68 DR. G. C. BOUENE ON THE RANINIDiE : 
Though Notosceles is in several respects intermediate between Notopoides 
and Raninoides, the last-named genus (figs. 5 & 6) has many distinctive 
features, most of which may be explained as adaptations to a swimming- 
habit. The carapace is elongated, and its flanks taper so evenly posteriorly 
that it may fairly be described as boat-shaped. The first abdominal tergum 
is notably narrower than the posterior margin of the carapace, and the whole 
abdomen is narrow and more distinctly flexed under the thorax than is usual 
in Eaninidaj. On the ventral surface there is a broad and long flat plastron 
in the formation of which the eleventh and twelfth sterna take an even larger 
share than the tenth (fig. 6). The twelfth sternum is of considerable length 
antero-posteriorly and is also broad and nearly flat. The articular cavities 
of the second pair of pereiopods are placed at its hinder border and face 
backwards. The thirteenth sternum being very short, the articular cavities 
of the third pereiopods are close to those of the second, and the two pairs of 
limbs, whilst closely contiguous to one another, are separated by the whole 
lenoih of the twelfth sternum from the first pereiopods. The last pair of 
pereiopods are so reduced and slender that they are usually described as fili- 
form ; they terminate in minute pointed dactyli. The reduction of the last 
pair of legs and the narrowing of the base of the abdomen seems to be cor- 
related with the suppression of the posterior branchial orifices ; at any rate, 
I can find no trace of these orifices in Raninoides. Nor could they be of 
much service if present, for the external water conduits which in other 
forms admit of a flow of filtered water to these orifices are here wanting. 
Thouoh the eleventh, twelfth, and thirteenth thoracic epimera are as much 
exposed to the surface in Raninoides as in other Eaninidse, they are not con- 
cave and are scarcely overhung by the edge of the branchiostegite. The 
epimeron of the eleventh somite is relatively small, and so far from being- 
concave that it is slightly convex. The epimera of the twelfth and thirteenth 
somites are obliquely grooved, and into these grooves the meri of the second 
and third pereiopods, when bent forwards and pressed against the sides 
of the body, fit so closely that no water can pass between. The first 
pair of pereiopods are slender, and when at rest are directed forwards, 
their large cordate dactyli being pressed against the bases of the cheli- 
peds. Their function is obscure, but probably they are used for digging. 
The characters of the second and third pereiopods are clearly shown in 
fig. 6. In these limbs the coxa and basis are directed backwards : the short 
ischium is nearly transverse to the long axis of the body : the merus is long 
and slender : the carpus normal, but it is to be observed that both it and the 
merus are scantily furnished with short hairs. The propodus and dactylus 
are flat and greatly expanded and the " fan-hinge " between them 
is a noticeable feature. A fringe of long stiff hairs is borne on the 
hind edge of the propodus and on the inner margin of the dactylus. The 
