﻿T. Davidson — On New Scottish BracMopoda. 15 



may mention that although the external character of the genus 

 and some of its internal ones have been carefully described, the 

 questions as to its affinities and muscular arrangements offer great 

 difficulties which 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 pi. vi. 

 fig. 4:d and c, and in fig. Ic and d, are drawn internal casts of Sipho- 

 notreta tmguicidata and S. fornicata, in which it is seen that the 

 muscular scars occupy a small space in the umbonal portion of the 

 interior of both valves ; but he fails to define these impressions or 

 explain their functions. 



During his recent visit to Brighton I asked Prof. F. Schmidt if 

 he could procure me a sharply-marked and well-preserved internal 

 cast of Siplionotreta unguicidata, and on his return to Eeval, in his 

 usual kind and obliging manner, he lost no time in sending me the 

 cast (Fig. 7) from the Lower Silurian Eocks (his " Schicht Id ") of 

 Keval. 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 them 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 Brachiopods, such 

 as Lingida, 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 Monomerella, 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 Monomerella. 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. 



