108 Dr. A. Vau^liaii on Seinlimla. 



(2) Marked tratisvcrseness : Spirifer ambujaus i.s typically 



an elongated shell. 

 (•i) The sides of the shell have a continuously unit'oiin 



curvature: in Spirifer amhiguns the curvature is 



strong at the point of niaxiinuni width, but the outline 



heconies rapidly straight above and below that 



])oii.t. 

 (4) The fold is uniformly convex in transverse section : in 



S. amJ>iguus the section is flattened and usually 



excavated on the top of the fold. 

 (.')) The fold is strongly semiconical and extends to the 



1 eak : a chaiacter very conunon in the Spiriferids, 



but almost unknown in the Athyrids. 



(6) A short straight hinge-line, extending the width of 



the beak of the brachial valve (as indicate I by the 

 approximation of the valve-intersection to a horizontal 

 direction on either side). 



(7) The absence of any concentric growth-halts and com- 



plete smoothness : Seminula usually exhibits strong 

 concentric growth-halts. 



The depiction of a perforated beak is quite negligible, for 

 the perforation, as drawn, is much too large to be the unbroken 

 aperture of 6'. amhiguus^ and, unfortunately, specimens of 

 Martinia glabra with the beak perforated in this way are 

 sadly common. 



As a matter of mere personal experiencCj many specimens 

 of Martinia glabra may be collected which agree with Brown's 

 figure of Compositd ambigua, but I have never seen a specimen 

 of <S'. ambiguus which has any right to be identified with it. 



Hence it seems clear that, though undoubtedly Bri:)wn 

 thought tiiat his conception of Coniposita included Spirifer 

 ambiguus, Sow., he did so in error. 



Here is another problem for the expert in nomenclature! 

 Luckily, Martinia has precedence over Composita, and conse- 

 quently escapes the danger of rejection in favour of Brown's 

 genus. 



I sliould like to tender my thanks to Dr. Ivor Thomas, of 

 H.M. Geol. Survey, for assistance in exan)ining the Gilbertsoa 

 specimens, and also for pointing out to me, several months ago, 

 that Seminula was sickening for a serious illness. As 

 Dr. Thomas will probably explain his own views, I need say 

 no more beyond expressing the hope that my old aud trusted 

 friend Seminula will "pull through." 



