Kr EDE M A N N — S ESS1 LE Con LTLARIA. 



TO.". 



upper grooves, w here it is apparently least crushed, is almost smooth, w ith 

 only an obscure indication of transverse lines of fracture. On the sides it is 



broken into transverse ring segments. Although it is thicker than tl uter 



layer, it is more frequently lost, leaving, however, a smooth cast. 



The segmental line appears as a shallow groove, scarcely conspicuous in 

 most specimens. It therefore is of no help in identifying the young Conulariw, 

 Of greater importance in this regard is the structure of the grooves at the 

 edges of the pyramid, as this is generally the best preserved part of the fossil. 

 In the specimens, for instance, represented in Plate [, figure 4. and Plate 

 II, figure 5, the side walls of the grooves alone are preserved in the distal 

 part, the connecting wall being either dissolved, as indicated by the smooth 

 surface between the edges in Plate I, figure 4, or broken aw ay as in Plate 

 II, figure5. The w alls of the grooves are much thickened, this strengthening 

 extending also to the adjoining parts of the faces, so that the grooves are lined 

 by two thick ridges. The connection between fragile thin faces and stoul 

 edges seems to be found in other species also. Oonularia Lmnarssoni, Holm,* 

 is described as having the grooves stronger than the segmental line and 

 being fragile toward the aperture. 



As the original of Plate II, figure 5, show s at the upper groove, and as 

 has been observed in other species, the surface film extended — here with its 

 wavy transverse wrinkles — over the groove, covering and closing it (PI. II, 

 fig. 2, a). Where the outer layer is lost, but the underlying parts are fully 

 preserved, there appears next below a thin smooth layer (A) with indications 

 of transverse lines of fracture; this layer in its turn covers a milky while 

 laminated substance (phosphate of lime). The latter (<?) fills the groove and 

 contrasts strongly with the black shining w alls (d ). Often, how ever, this 

 substance is lost, leaving the groove empty or giving place to a tilling by iron 

 oxides. The side walls of the empty groove show mostly very marked 

 transverse fractures with upturned margins. The groove seen from the 

 inside ( PI. II, Fig. 3) has a roof-like form w ith strongly slanting sides, w hich 

 are either smooth or exhibit the same transverse joints as seen from the 

 outside. Sometimes oblique pressure caused these joints to be pushed over 

 each other. Where the top is broken off the white phosphate of lime 

 appears again. 



From these observations it may be stated that the edges of the pyramid 

 of Oonularia gracilis, Hall, formed a kind of supporting framework for the 

 faces ; that the grooves, therefore, had strong w alls which were continuous 



*0p. cit., p 130, Plate IV, figures 38-40 



