168 1>R. F. .T. XORTH OX [vol. lxxvi, 



by Davidson's figures, the ch*a wings are obviously incorrect, because, 

 although they are supposed to represent the same specimen seen 

 from above and below, in his fig. 4 the lateral portions of the 

 transverse plate are convex towards the area, while in his fig. 5 

 they are concave, so that the upper slit occurs at the bottom of 

 a semicircular trough. In the circumstances, we can only regard 

 Davidson's figures as misinterpretations of true Syringothyroid 

 characters, and it then transpires that De Koninck was the first 

 to call attention to the transverse plate and syrinx. 



No reasonable grounds exist for supposing that there are two 

 types of syrinx, the one occurring in Syringothyris cuspidata and 

 the other in Spirifer distans : for, in addition to the evidence 

 already adduced, the structures indicated in Davidson's figures 

 have not since been observed in any other specimen, and it is shown 

 elsewhere in this paper that Spirifer distans does not possess a 

 syrinx at all. 



In 1863, A. Winchell described a Spiriferid shell l (from the 

 yellow sandstones lying beneath the Burlington Limestone [Lower 

 Mississippian] at Burlington, Iowa (U.S.A.), which possessed a 

 plate-system in the ventral valve similar to that already noticed 

 by L. G. de Koninck ; and, apparently unaware of that author's 

 communication, made the character the basis of a new genus, to 

 which he gave the name Syringothyris, with S. typa Winchell 

 as the genotype. He described the syrinx-bearing plate in the 

 following terms : — 



' transverse plate connecting the vertical dental lamellae, arched above, and 

 beneath giving off a couple of median parallel lamellae which are incurved so 

 as to nearly join their inferior edges, thus forming a slit-bearing tube which 

 projects beyond the limits of the plate from which it originated into the 

 interior of the shell.' 



Two years later, F. B. Meek announced the discoveiy of a similar 

 structure in ' Spirifera cuspidata'' from Millicent (Kildare). 2 



In 1868, W. King published a ' Monograph of Spirifer cuspi- 

 datus Martin,' in which he described in detail the characters of 

 the species, and figured a series of sections across the beak of the 

 ventral valve at various distances from the apex, illustrating more 

 clearly than had hitherto been done, the structure of the transverse 

 plate and syrinx. 3 



The precise nature of the transverse plate and syrinx, and their 

 relation to the delthyrial supporting-plates and to the apical 

 callosity, was described by me in 1913. 4 



The classification of the American members of the genus has 

 been discussed by Schuchert 5 and by Weller 6 . 



The shell-structure of Syringothyris. — The microscopic 

 structure of the shell of Syringothyris gave rise to a discussion 



1 Winchell [38] p. 6. 



2 Proc. Acad. Nat. Sci. Philad. ser. 2, vol. ix (1865) p. 276. 



3 King [17] pp. 1-23. 4 North [251 PP- 397-99. 

 5 Schuchert [29]. « Weller [36]. 



