ON THE BRACHYUROUS DECAPODS OF 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 Ranina. 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. Analogies. ° TRIGONOSTOMA. 
Mycteris .. PINNOTHERINA. Shell orbicular. Dromuna—Ranina. 
GRAPSINA. Shell quadrilateral. DoripPina. 
CancRINA. Shell arcuated with feet often natatory. CorysTINA. 
PARTHENOPINA. Shell uneven with crested feet. CALAPPINA. 
INACHINA. Shell sub-triangular and generally spined. LEUCOSINA- 
3. The analogy between certain Znachina, such as Acanthonyx, and certain Leucosina, such 
as Vursia, 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 :— 
Trine TETRAGONOSTOMA. 
Stirpes. 
Normal Groupe. 1 INAcHINA. First joint of external antenne very large, forming the 
Triangular Crabs. greater part of the lower side of the orbit, and always 
BE SSI Ii rh soldered to the clypeus. 
Epistome very large. Cly- 
peus generally advanced in 
front. L 

i First joint of external antenne small, not soldered to the 
2 PARTHENUPINA. clypeus and not aiding to form the lower side of the 
Rocky Crabs. U orbit of the eye. 
3 CANCRINA. Tigellus of external pedipalps always inserted at the inner 
Arched Crabs. angle of their third joint. The scapes of the palpi 
Aberrant Groupe. unidentated on the inside. Shell arched in front. 
(Tigellus of external pedipalps inserted at the outer angle, 
J or at the middle of the third joint. The scapes of 

4 GRAPSINA. 
BRACHYRHYNCHA. 
Square Crabs. > 
Epistome short. Clypeus L palpi not dentated. Shell quadrilateral. 
rarely advanced in front. Tigellus of external pedipalps always inserted at the sum- 
iP aaa J mit, or at the outer angle of their third joint. The 
NS) \__ scapes of the palpi not dentated. Shell orbicular. 
4. By Eurynome we pass from the Inachina to the Parthenopina ; by means of Athra we pass 
from the Parthenopina to the Cancrina ; from these to the Girapsina by Thelphusa ; from the 
Grapsina to the Pinnotherina by means of Doto; and from the Pinnotherina we return 
to the Inachina by means of Elamene. The following appear to be the families of Ina- 
