ON THE BRACHYUROUS DECAPODS OP THE CAPE. 
55 
the following descriptions I shall rarely allude to colour, since experience has taught me that in 
this respect dried specimens of Crustacea are not to be trusted. I would also observe, that as the 
groupes of degree next inferior to families — namely, genera — have never been worked out in this 
class, I have for the present considered almost all the various groupes under families to be sub- 
genera, although some of them, such as Plagusia, may possibly be a true genus, and others again 
may prove to be only sections of some sub-genus. I do not think that our collections, as yet, 
possess a sufficient quantity of species to allow us to decide what are the genera and what are 
the sub-genera of Decapod Crustacea. Professor Dehaan, however, has offered some valuable 
hints on the subject, and to those I refer the reader. We appear to enter among the 
Brachyura by the genus Mycteris, and to leave it by means of the genus Banina. There are 
ten Brachyurous stirpes, which may be placed in two columns, so as to shew those analogies 
which by Milne Edwards and others have too often been taken for affinities. 
TETRAGONOSTOMA. 
Mycteris ..Pinnotherina. 
GrAPSINA. 
Cancrina. 
Parthenopina. 
Inachina. 
Analogies. 
Shell orbicular. 
Shell quadrilateral. 
Shell arcuated, with feet often natatory. 
Shell uneven with crested feet. 
Shell sub-triangular and generally spined. 
trigonostoma. 
Dromiina — Ranina. 
Doripfina. 
Corystina. 
Calappina. 
Leucosina. 
3. The analogy between certain Inachina, such as Acanthonyx, and certain Leucosina , such 
as Nursia, is so great as to have induced M. Latreille to imagine that a direct affinity existed 
between the two groupes. In general, the above analogies appear reversed ; but the Tetra- 
gonostomous stirpes may be characterized as follows : — 
Tribe TETRAGONOSTOMA. * 
stupes* 
TFirst joint of external antennae very large, forming the 
J greater part of the lower side of the orbit, and always 
! soldered to the elypeus. 
r First joint of external antennae small, not soldered to the 
elypeus and not aiding to form the lower side of the 
orbit of the eye. 
f'Tigellus of external pedipalps always inserted at the inner 
<j angle of their third joint. The scapes of the palpi 
I unidentated on the inside. Shell arched in front. 
( Tigellus of external pedipalps inserted at the outer angle, 
t 1 or at the middle of the third joint. The scapes of 
palpi not dentated. Shell quadrilateral. 
rTigellus of external pedipalps always inserted at the sum- 
mit, or at the outer angle of their third joint. The 
^ scapes of the palpi not dentated. Shell orbicular. 
4. By Eurynome we pass from the Inachina to the Parthenopina ; by means of jElhra we pass 
from the Parthenopina to the Cancrina ; from these to the Grapsina by Thelpliusa ; from the 
Grapsina to the Pinnotherina by means of Dot.o ; and from the Pinnotherina we return 
to the Inachina by means of Elamene. The following appear to be the families of Ina- 
Normal Groupe. 
Oxyrhyncha, M. E. 
Epistome very large. Cly- < 
peus generally advanced in 
front. 
Aberrant Groupe. 
Brachyrhyncha. 
Epistome short. Clypeus 
rarely advanced in front. 
Inachina. 
Triangular Crabs. 
Parthenopina. 
Rocky Crabs. 
Cancrina. 
Arched Crabs. 
Grapsina. 
Square Crabs. 
Pinnotherina. 
Parasitical Crabs. 
