A STUDY IN CARCINOLOGY. 27 
Oxystoiiiata into a division (Abtheilimg) equal in value to llie Droniiidea 
(Boas's Droniiacea) and the Brachyui'a, the last-nameil division including all 
other true crabs. This arrangement, with some minor modifications, has been 
adopted by Alcock (1, 1896), Borrodaile (13, 1904), and Caiman (23, 1909). 
Against these authorities must be set the opinion of A. Milne Edwards and 
Bouvier, quoted above, and the similar judgment o£ Boas that the Raninidse 
cannot be included in the Oxystomata. But if carcinologists differ as to the 
ex;ict position that the Eaninidaj should occupy among the crabs, it is now 
generally agreed (except Ortniann [42], who keeps the Oxystomata apart 
from the Brachyura) that they are true crabs belonging to the section 
Brachyura and not to the section Anomura of the Uecapoda reptantia. 
Indeed, this was clearly established by de Haan seventy years ago, and it 
will be convenient to enumerate here the Brachyuran characters of the 
Raninidfe, most of which were recognised by the clear-sighted author of the 
volume 'Crustacea' of the ' JB'auna Japonica.' They are : — (1) Tlie reduced 
abdomen and the absence of uropods. (2) The absence of pleopods on the 
first abdominal somite of the female. (3) The absence of posterior abdominal 
appendages in the male. (4) The union of the pterygostomial region of the 
carapace with the epistome. (5) The adherence of the branchiostegite to 
the thoracic epimera. (6) The reduction of the branchise. (7) The absence 
of an exopoditic scale on the second antenna. (8) The presence of a sella 
turcica posterior. (9) The expansion of the ischium and merus of the third 
maxillipeds to form a plate-like covering to the other mouth-parts. (10) The 
presence of orbits in which the eye-stalks can be concealed, and correlated 
with this the reduction in size of the first and second antenna;. Other 
characters might be mentioned, such as the specialisation of the thoracic 
limbs as organs of locomotion, involving a great development of the apo- 
demes forming the walls of the cavities in which the muscles of the limbs are 
contained. In other words, it is part of the distinctive facies of a crab that 
the musculature is highly developed in connection with the locomotory 
thoracic limbs, and is feeble almost to the point of disappearance in the 
abdomen. This feature is strongly marked in the Raninidaj. 
On the other hand, it is generally recognised that the Raninidse exhibit a 
number of Macruran characters which, on the assumption that the Brachyura 
are descended from the Macrura, are primitive. Among the more important 
of these are : — The comparatively well-developed rostrum, which, however, is 
absent in Cosmonotus. The proximal segments of the second antenna are 
not fused with the epistome, a primitive feature also shared bj^the Dromiacea. 
The presence of a sternal canal and the relatively well-developed anterior 
thoracic apodemes. The narrow and keel-like posteiior thoracic sternites. 
The oviducal apertures opening on the coxse of the third pereiopods, another 
primitive character shared with the Dromiacea. The external lobes of the 
