206 DR. F. J. NOBTH ON [vol. Ixxvi, 



Tylothyris subconica is, therefore, connected by intermediate 

 forms with the Lower Avonian species, T. laminosa, from which it 

 undoubtedly descended. So far as I have been able to ascertain, 

 there are no representatives of Tylothyris in Permian or newer beds, 

 and, as in the case of Syringothyris, its pre- Carboniferous history 

 in Britain is at present unknown. 



V. The Relation between Sph:ifeiuxa and 

 Stringoth YSIS. 



The late Dr. Arthur Vaughan, in his ' Bristol Paper,' compared 

 certain Spirif eroid shells from the ' Upper Tournaisian ' of the Avon 

 section with M'Coy's species ' Spirifera laminosa,'' and later 

 [35] p. 43, definitely expressed the opinion that they did indeed 

 belong to that species, an opinion which has now been fully con- 

 Jirmed. Dr. Vaughan, however, referred the species to the genus 

 Syringothyris, remarking, [33] p. 301, that 



' within the delthyrium there is a distinct rostral callus and a trace of a 

 syrinx. I have not as yet obtained unequivocal proof of the existence of 

 a syrinx, but the presence of the rostral callus is indisputable.' 



In a later paper, [281 »p. 383. he stated that 



' wholly or partly buried within this callus is an infilled syrinx that can 

 be seen half projecting along the middle line of the callus, and in weathered 

 specimens is represented at the apex by a short narrow rod. A cross- 

 section near the beak shows the infilled syrinx and the dental-plates ; at a 

 little distance below the beak the strong mesial septum begins to appear.' 



No specimen that I have examined affords any justification 

 for assuming the existence of a syrinx embedded in the apical 

 callosity, and in the absence of a figure it is impossible now 

 to determine the precise nature of the structure to which Vaughan 

 referred. His allusion to a short narrow rod seen in the apex of 

 weathered specimens suggests that it may have been the edge of 

 the median septum projecting through the upper surface of the 

 apical callosity ; but, in any case, it cannot have been comparable 

 with the syrinx of Syringothyris, for the following reasons : — 



(1) The essential characters of Syringothyris do not appear in sections 



immediately under the beak. (See fig - . 1 a, p. 166.) 



(2) There is no elevated median septum in the ventral valve of Syringo- 



thyris. 



(3) The two structures, a median septum and a syrinx-bearing transverse 



plate, could not coexist in the same shell, since they would mutually 

 interfere one with the other. 



(4) Sections (see figs, lm & 1 n, p. 166) across the beak of Tylothyris 



laminosa clearly show that it is not a Syringothyris. 



(5) No known specimen of Syringothyris has the imbricate ornament of 



T. laminosa. 



Vaughan recorded the close connexion between the species 

 T. laminosa and T. subconica in the following terms : — 



' S. subconica is so similar to S. laminosa- that its specific separation has 

 been viewed with scepticism. There seems, indeed, to be no reasonable doubt 



