part 2] SYMNGOTHYIUS AND SPIHTFEMKd . 191 



The existence of a transverse plate in a Devonian Spirifer does 

 not of necessity indicate an ancestor of Syringothyris ; for, as is 

 shown elsewhere in this paper, such a structure occurs in a number 

 of species of Spirifer, and, furthermore, the plicated fold and sinus 

 clearly indicate that the species under consideration has no con- 

 nexion with Wine-hell's. 



Spirifer distans J. de C. Sowerby. 



1825. Spirifer distans J. de C. Sowerby [32] p. 152 & pi. ccccxciv, fig. 3 (two 



figures). 

 1844. Oi/rtia distans Sowerby, M'Coy [20] p. 136. 

 1858. Spirifer distans Sowerby, Davidson [4] pi. viii, figs. 1-16. 

 1880. Syringothyris distans Sowerby sp., Davidson [5] p. 281 & pi. xxxiii, 



figs. 4-5'. 



The fossils which have been described under this name seem to 

 incluele more than one species, and they have been regarded as 

 Syringothyris, although none of them really belong to that genus. 



They ail agree in having more or less clearly-defined plications 

 on the fold and sinus, a character which in itself is sufficient to 

 suggest that they are not species of Syringothyris. 



The locality of the holotype of the species is recorded by Sowerby 

 as 'Dublin,' and although it has also been noticed in other parts 

 of Ireland, there do not appear to be any forms in the Carboni- 

 ferous Limestone of England and Wales that can be definitely 

 referred to this species. 



Spirifer distans exhibits considerable variation in the length of 

 the hinge-line. Some specimens, as, for instance, Sowerby's 

 holotype, closely resemble a normal Spirifer, but other examples 

 have a relatively longer hinge-line and a less incurved area. 



Sp. distans differs from Syringothyris in many respects. In 

 general appearance the shell bears a much closer resemblance to 

 Spirifer. The lateral slopes of each valve are more tumid, and 

 the area is less elevated and more incurved than in Syringothyris. 

 (This more especially applies to forms like Sowerby's holotype, 

 because in the height and curvature of the area some examples 

 resemble the form of Syringothyris found in the Zaphrentis 

 Zone of the South- Western Province.) The apical angle of 

 Sp. distans is greater, from 120° to 125°, as against 95° to 105° in 

 S. cuspidata ; the delthyrial fissure is proportionately narrower, its 

 sieles diverging at an angle of about 16°, while in Syringothyris 

 the corresponding angle is about 25°. The delthyrial supporting- 

 plates are situated almost at right angles to the plane of the 

 cardinal area, and in consequence of the narrow fissure appear in 

 sections across the beak of the ventral valve as a pair of nearly 

 parallel plates, much closer together than is the case with Syringo- 

 thyris (see fig. 1 k, p. 166). There is in Sp. distans no threefold 

 division of the area, which is marked by vertical striations through- 

 out its entire length. 



The fold is very little elevated, and makes a much less pronouncd 

 wave in the anterior margin than in Syringothyris. The costae, 



