218 SUPPLEMENT TO THE 



obliging manner, lie lost no time in sending me the mncli desired example. I published in 

 vol. iv., new series, of the ' Geol. Mag,' for January, 1877, enlarged figures of this internal 

 cast, which showed that the muscular scars occupied a small space in the umbonal 

 portion of both valves. Although the impressions were tolerably well defined, neither 

 Prof. King or myself could interpret them as clearly as we desired, and more material 

 will be required before that can be satisfactorily achieved. 



It is quite evident, however, that the genns belongs to King's division Tretenterata^ 

 or to that group of Brachiopoda, such as Lintjula, which are destitute of an anal aperture , 

 and it appeared to both of us that the specimen we have been able to examine favour 

 the idea that Siphonotreta is more closely related to Oholus and Discina than to Mono- 

 merella, though the last genus may still lay some claim of being its kindred. 



We all know that Oholus has a large muscular scar («) close to, and at each end of, 

 the edentulous hinge on both valves ; each scar is separated from another ib), much 

 elongated by a ridge (e). Professor King thinks the two ridges are present in the 

 internal cast sent to me by Prof. F. Schmidt, 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 of Obolus. In Oholus the scar a is well pronounced, lying 

 outside of, and distinctly separated from, the ridge. In Biscina there are two posterior 

 adductor muscles, leaving strong scars similarly situated, and these Prof. King considers 

 to correspond to those of a in Oholus. 



If this be a correct interpretation as regards the scars at the origin of the ridge in 

 SvpJi07iotrela, the affinities of this genus, as above stated, will be more on the side of 

 Obolus and Discina than of Mommerella. Monomerella, as has been stated elsewhere by 

 Prof. King and myself, does not appear to have posterior adductors ; but they may have 

 been atrophied, thus causing the genus to be a little more removed than Siphonotreta 

 from Oholus and Discina. The muscular impressions in Obolus are more spread out 

 than in either Discina or Siphonotreta, and Prof. King thinks that this difference appears 

 to be explained thus : the latero-cardinal scars in Siphonotreta are more crowded together 

 than they are in Oholus, and the central projecting portion of the undercut, "spectacle- 

 like " impressions in Oholus advance more to the adductor margin of the valve than the 

 corresponding impressions in Siphonotreta. 



In Siphonotreta scotica the spines are very short and do not, any more than those 

 figured by Kutorga, show that peculiar raoniliform character so well described and figured 

 by Morris in the much longer spines of Siphonotreta anglica. 



Mr. J. F. Whiteaves, of the Geological Survey of Canada, has kindly sent for my 

 inspection three specimens of Siphonotreta from the Lower Silurian (Utica Slate or upper 

 part of the Trenton Limestone), near Ottawa City, Ontario, which in every respect 

 agree with the shell I have described under the name of Sipho?iofreta scotica from the 

 Llandeilo of Craighead, Girvan. The Canadian specimens measure 6 lines in length 



