F. J. North — The genus Syringothyris. 395 



of the differences between S. cuspidata, Martin, and S. typa, Winchell, 

 and also the identity of Syringothyris typa with Spirifer carter i. 

 Hall, the last-named, species, having priority, becomes the type-species of 

 the genus Stringothtiiis. 



The differences between Syringothyris carteri (Hall) and S. cuspi- 

 data (Martin), as defined by Schuchert, are confined to external 

 characters, and are as follows : the area of the pedicle valve is flat or 

 concave in S. carteri, while in S. cuspidata it is usually reclined ; 

 and in S. carteri the lateral slopes of the pedicle valve are slightly 

 convex, while in S. cuspidata they are flat or nearly flat. These 

 differences are practically the same as those between Syringothyris 

 aff. cuspidata, of authors, from the Cleistopora and Zaphrentis zones 

 of the South-Western Province, and Martin's specimen from the 

 Visean of Castleton, or S. cuspidata from the Carboniferous Limestone 

 [Syringothyris-zone?) of Kildare. 



Winchell did not figure any of his specimens, but Syringothyris 

 typa has been figured by Hall & Clarke ^ and S. cuspidata by 

 Davidson ^ and King ^ 



3. General Account of the Plate-like STRtrcTUKES in the Pedicle 

 Valve of Syringothyris. 



(1) The Belthyrium and Pseudodeltidium. — The cardinal area in the 

 pedicle valve of Syringothyris is interrupted by a triangular del- 

 thyrium as in other brachiopods. It is only on rare occasions that 

 any plate is preserved covering the delthyrium, but occasionally the 

 delthyrium is partly closed by a convex pseudodeltidium, the distal 

 end of which is concave towards the apex of the shell, leaving 

 a semicircular opening between itself and the hinge-line. Specimens 

 in which this plate is preserved have been figured by Hall & Clarke * 

 and Davidson.* "When the pseudodeltidium has been lost two grooves 

 into which its edges fitted can often be seen, one on eitlier side of the 

 delthyrium. 



In Syringothyris cuspidata the pseudodeltidium has no foramen 

 such as occurs in Cyrtid. Davidson® figured an internal cast of 

 a pedicle valve from the Carboniferous Limestone of Breedon Hill, in 

 which, he maintained, "the deltidium was in reality perforated by 

 a circular foramen." His specimen shows, however, not a foramen 

 in the pseudodeltidium, but a cast of the syrinx characteristic of 

 Syringothyris. 



Some authors, for example, King'' and more recently Woods ^ and 

 Cowper E.eed,^ have used the term deltidium for the covering plate 



^ Hall & Clarke, 1894, pi. xxvi, figs. 6, 7, 10 ; pi. xxvii, figs. 1-3. 

 ' Davidson, vol. ii, pi. viii, figs. 19-24; pi. ix, figs. 1, 2; vol. iv, pi. xxxiii, 

 figs. 1-3. 



^ King, 1868, pis. ii, iii. 



* Hall & Clarke, 1894, pi. xxvii, fig. 15. 



^ Davidson, vol. iv, pi. xxxiii, fig. 1. 



^ Davidson, vol. ii, pi. viii, footnote, and pi. ix, fig. 1. 



■^ King, 1850. 



^ Woods, Palaeontology, Invertebrate, p. 157. 



^ Cambridge Natural History, vol. iii, p. 498, 1895. 



