Dr. H. Woodward—Prosopon in the Clypeus- Grit. 81 
emarginate. There is no evidence of any abdominal or caudal segments 
having been preserved, the ventral surface being firmly imbedded in 
very bard matrix. 
There is evidence of the presence of four minute rounded tubercles 
on the surface of the cardiac region (C.), but as the carapace is 
decorticated it may have had other small papillee upon its perfect test. 
No appendages of any kind are preserved. 
Formation.—‘ Clypeus-Grit,” Inferior Oolite. 
Locality.—Tor Hill, near Wotton-under-Edge, South Cotteswolds. 
Collection.—Mr. Linsdall Richardson, Cheltenham. 
Remarks.—Although, thanks principally to the memoir of Herman 
von Meyer (1859), we are acquainted with quite a number of small 
carapaces of Crustacea of an oblong-oval form, from strata somewhat 
similar in character and age to that now under consideration, it is 
difficult without a knowledge of their appendages or the ventral 
surface of the carapace to place such forms more than approximately 
in their natural family, in relation to existing forms. There is, too, 
a strong tendency amongst these earlier Secondary Crustacea to present, 
in the same individuals, characters observed to be peculiar to distinct 
families in more modern times. Sayin 
Thus it becomes difficult in the species of the genus Prosopon, which 
are only known by their carapaces, to refer them to the “Maioidea 
(=Oxyrhyncha), the Leucosiidea (=Oxystomata), or to the Anomura 
(= Anomala), to each of which groups they seem to show synthetic 
relations. 
In the evolution of the. short-tailed crabs (Brachyura) one feature 
of great interest is the very noticeable change in the form of the 
carapace or cephalothorax. Thus in most modern crabs the body is 
broader than it is long, but in the earliest forms it is longer than 
broad. If the elongation of the cephalothorax is further accompanied 
by the exposure of the abdomen, which in most of the section Brachyura 
is quite small and carefully concealed beneath the cephalothorax, then 
the division between the short-tailed crabs (Brachyura) and the long- 
tailed lobsters and prawns (Macroura) disappears, and they become 
one group (the Decapoda). Ay 
No crabs are met with after the close of the Secondary period, but 
the Macroura are found in the Carboniferous rocks. These show 
evident signs of a further modification in structure, and we find many 
characters of the Schizopoda (the Squillide and Myside) incorporated 
into the Macrouran Decapods of the Coal period. Thus the Poporx- 
THALMA (stalk-eyed Crustacea), which exist now and in Oolitic times 
as three distinct suborders, were apparently represented in earlier post- 
Carboniferous times by two and in Carboniferous times by only one 
order. In point of fact, it is amongst these earlier individual forms 
of Arthropods that we should naturally expect to find those more 
generalized characters which occur in several distinct types only 
at a much later period in geological time. 
T dedicate this little crab to Mr. Linsdall Richardson, who has 
devoted so much time to the unravelling of the stratigraphy of the 
Inferior Oolite of the South Cotteswolds of the Bath—Doulting district. 
DECADE V.—VOL. IV.—NO. I. 6 
