from Homola in having a more ovoid carapace, a more developed rostrum, feebler legs, and especially in the form of the eyes which are very small and not narrowed at the base.

Here also should perhaps be placed some Australian species of the genus Paratymolus, Miers, 1879, in which the carapace is deflexed in front, flat behind, with the sides nearly straight, the 'front' being prominent and narrow. For a new family Paratymolida Mr. Haswell gives the characters, 'carapace in general form similar to the Maioidea. External maxillipedes partly over the epistome.' He thinks that it would perhaps be better placed among the Corystoidea. Mr. Miers, however, does not agree with this view, but thinks that it ought to stand near the Dromida. It is an argument the more for including the present tribe in the Brachyura, that two experts should be unable to agree whether a genus belongs to it or another tribe which is brachyuran beyond question.

Legion 2.-Ranininea.

The carapace is ovate-oblong, with the regions not defined, and the front' of varying width. The orbits are well marked. The first antennæ are without special fossettes, and are placed to some extent behind the second pair. The third maxillipeds are moderately elongate. The sternal plastron or breastplate is wide anteriorly. The walking-legs have the terminal joint broad and compressed; the last pair of legs are small and subdorsal in position. The vasa deferentia of the male are protruded. The pleon is short, partially extended, not folded under the trunk, with four pairs of appendages in the female.

Dr. Henderson includes the epithet 'smooth' in the description of the carapace, but this is obviously unsuited to Ranina scabra.

Dr. Boas has ingeniously suggested that the position of the vulvæ in the bases of the legs instead of in the sternal plastron has been brought about by the extreme narrowing of the plastron, and this may well have been

so, though such a species as Petalomera pulchra in the preceding legion does not seem to suit the theory. One may, however, suppose that in some instances a re-widening of the plastron may have been developed without any rearrangement as to the position of the vulvæ.

This legion contains the single family Raninidæ, for which, therefore, no separate character is needed. It includes some nine genera, limited to the warm seas, and inhabiting chiefly the tropics, with a range of depth apparently not exceeding 300 fathoms.

Ranina scabra (Fabricius), originally called Cancer raninus, Linn., and afterwards Ranina serrata, Lamarck, and Ranina dentata, Latreille, from Amboina and the Sandwich Islands, was known to fame long before a separate genus was established for it. The carapace has been compared to an inverted triangle. It is very broad anteriorly, but the sides slope very gradually to the rounded hinder margin. The eye-stalks are three-jointed, strongly geniculate, and have a very deep orbit. The pterygostomian regions of the carapace unite with the sternal plastron so as completely to separate the third maxillipeds from the chelipeds. The plastron itself is anteriorly almost trefoil-shaped, but to the rear becomes linear. The branchiæ, Milne-Edwards says, are arranged as in the Brachyura, but in the conformation of the respiratory cavity there is a peculiarity of which he knew no other example. As in the Leucosiidæ, the carapace is joined to the sternum and the cavity of the sides, without leaving above the base of the feet or maxillipeds any space for the entrance of the water necessary for breathing, but the afferent channel instead of being pierced beside the efferent channel, on the sides of the mouth, is situated behind and has a special opening below the base of the pleon. This view, however, is criticised by de Haan in a passage that is not free from perplexity. 'In Portunus and Grapsus,' he says, 'the water is brought to the branchiæ by a double path and removed by a double path; it reaches the branchial cavity by the mouth and the apertures near the base of the chelipeds; but it passes out both by the space between the inferior lateral margin

A DISCUSSION ON BREATHING

141

of the trunk and the epimera and by two ducts under the insertion of the pleon. In Ethusa the case is the same.

FIG. 11-Ranina scabra (Fabricius), a male specimen, with separate figure of the pleon

In Calappa and Matuta the hinder ducts are not below but close to the pleon over the first joints of the fifth pair of

legs. In Dorippe, Leucosia, and Ranina, the lower border of the trunk closely coheres with the epimera (compare Milne-Edwards, vol. 2, p. 193). In the first the anterior apertures, in which the first joints of the third maxillipeds work, are remote from the base of the chelipeds; but in the following they are altogether wanting; so that these have only one path on each side by which the water reaches the branchiæ, and one by which it is withdrawn. The hinder ducts in Ranina are broader than in other families and amplified by lateral apophyses, but otherwise in Portunus and Grapsus they are in the same place. The water appears to enter the branchial cavity by the anterior apertures, and to issue by the hinder ones, and not to have a diverse or in Ranina and Leucosia a contrary motion (compare Milne-Edwards, vol. 1, p. 88, vol. 2, p. 194). In the anterior part there is a force, namely the movement of the maxillipeds, by which the water is brought in; that being expelled behind, follows the movements of the body; the apertures beside the base of the chelipeds and the branchial appendages of the maxillipeds are ciliated on the margin, and by these cilia alien bodies are kept away from the branchiæ, when water is brought to them from in front, whereas [they would be] of no use but a hindrance to breathing, were the water brought from behind.'

Fritz Müller refers to the statement made by MilneEdwards about the breathing arrangements of Ranina, but does not mention de Haan's contrary opinion. Fritz Müller himself unfortunately had not had an opportunity of personally investigating the question Judging from MilneEdwards' figure of Ranina dentata, it would appear to have an arrangement of the pterygostomian regions not unlike that already described in the genus Sesarma, by which the crab when on dry land is enabled for a long time to go on breathing the same small stock of sea-water. Such an arrangement would undoubtedly be convenient for the Ranina, if the story be true that it has a decided propensity for climbing on to the roofs of houses. MilneEdwards attributes this story to Rumphius, but nothing of the kind appears to be included in that author's account

DOG-CRAB AND FROG-CRAB

6

143

of his Cancer raniformis, though in the next preceding description he tells of a swift-running dog-crab,' Cancer caninus, which is said to burrow under houses and enter them. When the limbs of Ranina are drawn together it is said to look not unlike a frog, a resemblance to which the generic name points, as well as the trivial name of frogcrab, and the specific name raniformis given it by Rumphius.

Kaninoides, Milne-Edwards, 1837, is nearly allied to Ranina, but has the last pair of legs very short and threadlike instead of equal in size and similar in shape to the preceding flattened pair. In Raninoides personatus, Henderson, the pterygostomian areas are described as being strongly granulated as well as slightly pubescent, and the same is said of the type species of a new genus, Notopoides latus, Henderson, 1888. In the female of this species there is an ovoid median opening in the sternum, between the third and fourth pairs of legs. Raninoides personatus has a similar opening but of very small size. The function of these apertures does not appear to have been explained.

Notopus, de Haan, 1841, includes several species, in which the last pair of legs are of moderate size, not filiform. As the name of the genus implies, their position is dorsal, and this, though a character common to the family, is again emphasised in the specific name of Notopus dorsipes (Fabricius). Of a crustacean allied to this, Darwin, in his 'Naturalist's Voyage,' gives the following account: During our different passages,' he says, 'south of the Plata, I often towed astern a net made of bunting, and thus caught many curious animals. Of Crustacea there were many strange and undescribed genera. One, which in some respects is allied to the Notopods (or those crabs which have their posterior legs placed almost on their backs, for the purpose of adhering to the under side of rocks), is very remarkable from the structure of its hind pair of legs. The penultimate joint, instead of terminating in a simple claw, ends in three bristle-like appendages of dissimilar lengths the longer equalling