R. I. Pocock—Carboniferous Arachnida. 511 
that the other specimens described by Scudder as G. carbonarius were 
correctly referred to the genus Geraphrynus, despite the opinion of 
Hansen, | have nothing further to say about them. I cannot find any 
characters to justify the separation of Madrachne, Melander,’ from 
Geraphrynus. 
4. Geratarbus was based upon two species, G. scaber and G'. lacoet, 
which apparently belong to different orders of Arachnida, G. scaber 
being probably one of the Ricinulei. I select G. lacoe, therefore, as the 
type. Judging from the figure and description of G. lacoei, it seems 
that the posterior border of the carapace in Geratarbus is straight; the 
opisthosoma has nine terga, of which the anterior five are short and 
straight from side to side and the posterior four much longer, gradually 
increasing in length from the sixth to the ninth, the ninth equalling 
the sum of the seventh and eighth. The sternal area of the prosoma 
is narrow and elongate, and the coxe of the first pair of legs meet 
only at their proximal ends and diverge at an acute angle. Geratarbus 
differs from Geraphrynus and Architarbus in the straightness of the 
posterior border of the carapace and of the anterior terga of the 
opisthosoma, in the difference in relative size of the posterior terga, 
and in the divergence of the anterior coxe. 
5. Opilotarbus, nov. Carapace evenly rounded in front, its postero- 
lateral angles squared, and its posterior border straight. Opisthosoma 
nearly parallel-sided, somewhat widely rounded at its anal extremity, 
with apparently the normal number of sterna but only eight terga, of 
which the anterior five are short and straight and the posterior three 
verylarge. Sternal area of prosoma small, oval, longer than wide. Coxe 
of legs of first pairin contact throughout. Type, Architarbus elongatus, 
Scudd.,? 1890, from Mazon Creek, Braidwood, [llinois. 
Fritsch * published figures and descriptions of what he believed to 
be the dorsal and ventral views of Scudder’s type of this species. 
So far as the dorsal surface is concerned this view is probably correct ; 
but it is perfectly clear that the figure of the ventral side, if 
approximately accurately drawn, was taken from another specimen. 
I have no doubt that it represents a species of Geraphrynus. Neither 
in its proportions nor in the position of its limbs ‘can it be made to 
agree with Emerton’s figure of the ventral view of the type or with 
Fritsch’s own figure of the dorsal view of the latter. 
Opiliotarbus has the posterior border of the carapace and the anterior 
terga of the opisthosoma straight as in Geratarbus, but it differs from 
that genus in having only eight terga on the opisthosoma, of which 
five are short and three very long. 
When the characters of the genera above described are analysed, 
it seems that Phalangiotarbus stands quite apart from the others in the 
large size of the sternal plate of the prosoma and the wide separation 
of the coxee of the legs of the first pair. For this reason I propose to 
-follow Haase and refer it to a distinct family, Phalangiotarbide. To 
comprise the rest the family name Architarbide is available. 
In the following key to the genera I have juxtaposed them 
1 Journ. Geol. Chicago, vol. xi, p. 179, pl. v, fig. 1, and pl. vil, fig. 1, 1903. 
2 Mem. Bost. Soc. Nat. Hist., vol. iv, p. 449, pl. xl, fig. 1 (ventral view). 
3 Pal. Arachn., pp. 33, 34, fig. 374 (dorsal view), not fig. 37B. 
