170 DE. F. J. NORTH 05f [vol. lxxvi r 



are of this nature, and show no trace of punctae ; but, •wherever 

 the shells are suitably preserved, as (for example) in the Zaplir'entis 

 Zone in many parts of the South- Western Province, the punctate 

 structure is quite evident. 



(h) The Characters of the Genus. 



The shell of Syringothyris is Spiriferoid in form and variable 

 in size. The dorsal valve is slightly convex ; while the ventral 

 valve is more or less acutely pyramidal, owing to the presence of a 

 high cardinal area. 



The hinge-line is straight, and the cardinal extremities are 

 usually rounded, but are sometimes slightly produced and angular. 



The cardinal area is high, and either slightly concave, flat, or 

 even convex (see fig. 3, p. 17S). In the holotype of 8. cuspidata 

 the area is practically flat. The apical angle varies, but the 

 average for the genus is about 100°. 



In well-preserved specimens the area is clearly differentiated into 

 three regions by a pair of divergent lines extending from the apex 

 to the hinge-line. The whole area is marked by horizontal stri- 

 ations representing lines of growth, and the central portion bears, 

 in addition, vertical striations (see fig. 2). 



Fig. 2. — The threefold division of the area in Syringothyris 

 (diagrammatic), based upon the specimen figured in PL XIII, 

 Jig. 2. 



The central region of the area is bisected by a triangular delthy- 

 rium about three times as high as wide. The delthyrial angle 

 averages about 25°. The delthyrium is closed by a convex delti- 

 dium, 1 not perforated by a foramen as in Cyrtia. It is rarely 

 preserved in situ, but there are two grooves along the sides of the 

 delthyrium into which its edges are fitted. 



In the brachial valve there is a distinct, but low, convex fold,, 

 and in the pedicle-valve a corresponding concave sinus which 



1 In a previous paper (North [25] p. 395) I used, the term ; pseudo- 

 deltidium ' for this plate. I am indebted to Mr. H. Woods, F.R.S., for 

 pointing out that Von Buch introduced the term ' deltidium ' for the delthyrial 

 covering-plate in the Telotremata, to which Syringothyris belongs, and that 

 the use by American palaeontologists of Bronn's term ' pseudodeltidium ' in 

 this sense is incorrect. 



