66 DR. G. C. BOURNE ON THE RANINIDvE : 
Among otbev genera, Zanclifer and Notopoides, though their antennary 
flagella are not so much reduced, are in all essential respects so similar to 
Ranina that it can hardly be doubted that they have similar habits and are 
equally adaptable as regards their respiratory processes. Zanclifer differs 
from all other Raninidse in having normal, i.e. not feathered and differenti- 
ated, chelipeds, and it may be that it is more nearly related to the ancestral 
form than Notopus. It has all the external characteristics of a burrowing 
crab. Notopoides, on the other hand, is much more closely related to 
Notopus, from which it differs mainly in the elongation of the twelfth 
sternum, whereby the second, third, ai d fourth pereiopods are shifted back- 
wards and form a posterior group of legs, separated by a space from the first 
pereiopods : this feature is exhibited to a more marked degree in Notosceles 
(fig. 3) and is carried to an extreme in Raninoides (fig. 6). Tn each genus 
the increase in length of the twelfth sternum is correlated with a reduction 
in size of the last pair of pereiopods, a progressive narrowing of the abdomen, 
a reduction in the size and functional importance of the posterior branchial 
orifices, and progressive modifications of the second and third pereiopods 
indicative of their increasing use as swimming organs. A comparison of the 
series Ranina, Notopus, Notopoides, Notosceles, Raninoides, leads me to the 
conclusion that, whilst all of them are to a greater or less extent sand- 
burrowers, the first-named during its periods of activity progresses mainly 
by crawling and is a poor swimmer. Notopus and Notopoides crawl and 
swim ; Notosceles is a fairly efficient and Raninoides a very efficient 
swimmer. This conclusion I will now endeavour to justify. 
Notopoides is obviously a burrowing crab ; the sandy condition of the 
specimens in the Natural History Museum bears testimony to this habit. 
In most of the structural features subservient to the respiratory processes 
Notopoides bears a strong resemblance to Notojms. Attention may be 
directed specially to the following points : the last pair of pereiopods are not 
much reduced in size and all their joints are densely fringed with hairs ; the 
tergum of the first abdominal somite is as broad as the posterior margin of 
the carapace ; the posterior branchial orifices are patent and give evidence 
of their function as inhalant passages ; the exposed portions of the epiinera 
of the eleventh, twelfth, and thirteenth somites are concave and overhung by 
the edge of the branchiostegite ; the chelipeds are adapted for raking sand 
from under the thorax. In short, all the adaptations described in Notopus 
and Ranina for maintaining a respiratory current through the posterior 
respiratory orifices are present to an equal degree in Notopoides. This 
genus must be equally addicted to the burrowing habit, but the articulations 
and characters' of its last three pairs of pereiopods suggest that, when active, 
it is to some considerable extent a swimmer. 
In Notosceles the adaptations for maintaining a posterior inhalant 
respiratory current are still recognizable, but are obviously less efficient. 
