T. Davidson — On New Scotti-sh Brachiopoda. 
15 
may mention tliat although the external character of tke genus 
and some of its internal ones have been carefully described, tbe 
questions as to its affinities and muscular arrangements offer great 
difficulties wbicb the material in our possession does not allow us to 
solve in a satisfactory manner. The form and character of the 
perforated beak has been well described by Kutorga, and in pl. vi. 
fig. 4 d and c, and in fig. 7 c and d, are drawn internal casts of Sipho- 
notreta unguiculata and S. fornicata, in which it is seen that tbe 
muscular scars occupy a small space in the umbonal portion of tbe 
interior of both valves ; but he fails to define tbese impressions or 
explain their functions. 
Düring bis recent visit to Brighton I asked Prof. P. Schmidt if 
he could procure me a sharply-marked and well-preserved internal 
cast of Siphonotreta unguiculata, and on his return to Reval, in bis 
usual kind and obliging manner, he lost no time in sending me the 
cast (Fig. 7) fi - om the Lower Silurian Rocks (his “ Schicht Id ”) of 
Reval. Of this cast Figs. 8 and 10 are carefully enlarged represen- 
tations, 9 and 11 gutta-percha impressions taken from the cast, and 
likewise enlarged, to show in an approximately correct manner the 
character of the interior of both valves of the shell itself. 
After having made these drawings, I submitted thern and the cast 
to Prof. King, in order to have likewise his valuable opinion on the 
subject ; but although the impressions were tolerably well defined, 
neither of us could interpret them as we might have desired, and 
more material will be required before that can be satisfactorily 
achieved. It is quite evident, however, that the genus belongs to 
King’s division, Tretenterata, or to that group of Brackiopods, such 
as Lingula, which are destitute of an anal aperture ; and it appeared 
to both of us that the specimens we have been able to examine favour 
the idea that Siphonotreta is more closely related to Obolus and Discina 
than to Monomerelia, though the last genus may still lay some claim 
to being its kindred. We all know that Obolus has a large muscular 
scar (a) close to and at each end of the edentulous hinge in both 
valves ; each scar is separated from another one (b) much elongated 
by a ridge (c). Prof. King thinks the two ridges are present in the 
valve of Siphonotreta, and though the evidences on the valve are 
perplexing, there being appearances of two scars, or a compressed 
one, situated at the origin of the ridge, the evidence is somewhat 
in favour of the scar belonging to or representing the scar (a) 
in Obolus. That in Obolus the large scar (a) is well pronounced, 
lying outside of and distinctly separated from the ridge. In Discina 
there are two posterior adductor muscles, leaving strong scars simi- 
larly situated, and which Prof. King considers to correspond to those 
of (a) in Obolus. If this is a correct interpretation, as regards the 
scars at the origin of the ridge in Siphonotreta, the affinities of this 
genus, as above stated, will be more on the side of Obolus and Discina 
than of Monomerelia. Monomerella, as has been stated elsewhere 
by Prof. King and myself, does not appear to have posterior adduc- 
tors, but they may have been atrophied, thus causing the genus to be 
a little more removed than Siphonotreta from Obolus and Discina. 
