Lt. I. Pocock—Carboniferous Arachnida. 509 
the latter area which ‘‘crowds down the middle of the six following 
segments’; the sternal plates are the anterior ‘‘ triangular fragment ”’ 
sloping upwards to the ridge as well as the ‘‘ hinder portions with 
transverse scorings and ridgings”’ that ‘‘lie on a plane below”’; and 
the median ridge is the sternal area of the prosoma. In a crushed 
specimen confusion might easily arise between these dorsal and 
ventral elements of the skeleton. 
This interpretation, if correct, disposes of Haase’s view of the 
morphology of Architarbus. This author modified Scudder’s drawing 
to suit his idea that Architarbus belongs to the Amblypygous Pedipalpi. 
The anterior part of Scudder’s post-thoracic plate he regarded as the 
posterior sternal plate of the prosoma and its posterior part as the 
genital plate of the opisthosoma. Scudder’s drawing, however, does 
not justify Haase’s rendering of it, full of ingenuity though his 
interpretation was. 
Commenting on Haase’s opinion, Hansen states that of the three 
specimens figured by Scudder as G. carbonarius ‘‘only one, the one 
figured on pl. xl, fig. 12, can with any certainty be classed amongst 
the Amblypygi’’; and in an explanatory foot-note he adds that the 
figure shows eleven distinct sternites of exactly the same shape as 
those of Phrynus. This statement, however, is not true. No Phrynus 
has four narrow sterna following and curving round the genital plate 
nor the posterior sterna so well defined and large as shown in Scudder’s 
figure. Hansen, moreover, ignores the existence of the plates in front 
of the backwardly bulging plate which, by implication, he takes for 
the genital operculum; and he is compelled to assume that the first 
pair of appendages exhibited by the fossil has been quite wrongly 
drawn. He seems, in fact, to trust to the accuracy of the drawing 
where it compares favourably, as he thinks, with a Phrynus, and 
assumes inaccuracy where the discrepancies are irreconcilable. The 
figure admittedly resembles a Phrynus superficially. So much so, 
indeed, that I feel sure the artist, Mr. H. Emerton, made use of 
a Phrynus to help his delineation ; and this supposition is borne out 
by certain discrepancies between Scudder’s description of the fossil 
and KEmerton’s figure of it. 
The difficulties, then, that have hindered the understanding of the 
skeletal morphology of these fossil Arachnida are due to confusion 
between the dorsal and ventral elements. It appears to me that in 
nearly all cases the dorsal surface is exposed; but that owing to the 
removal or crushing of the carapace the underlying coxe and sternal 
area of the prosoma and the anterior sternal plates of the opisthosoma 
are also shown. ‘The figures of the following species bear out this 
view: Architarbus rotundatus,' Geraphrynus carbonarius,? Geraturbus 
lacoet,® Phalangiotarbus subovalis.* 
Judging from the figures published by Fritsch and Scudder of the 
species they name Geraphrynus (or Architarbus) elongatus, and from 
the material I have examined, I am convinced that in this group the 
1 Geol. Survey, Illinois, 1868, p. 568. 
2 Mem. Bost. Soc. Nat. Hist., vol. iv, pl. xl, figs. 1, 10, 12. 
Spline, tig. Lie 
4 Gzou. Maa., Vol. IX, p. 885, 1872 (Ph. ‘ Architarbus’ subovalis, H. Woodw.). 
