702 



Report of the State Geologist. 



section are compressed in the direction of the obtuse angles. The shell of 

 C. gracilis Hall, which I have seen only strongly compressed, therefore 

 probably had equal faces and a quadratic section. 



The complete flattening of the specimens without breaking, as well as 

 the common bending of the proximal parts of the shell (PI. I, fig. 4), are 

 indications of a slight flexibility of the shell. Hall's type also was "slightly 

 bent or arcuate." This remarkable character of C. gracilis is causally 

 connected with the extreme thinness of the walls already observed by Hall. 

 As the observation of small wall fragments (PI. I, fig. 6) and the 

 abundance of smooth casts of Conuinriw indicate, the wall was very easily 

 destructible. This may also account for the frequent absence of wall remains 

 in the young Oonularioe while the edges are preserved. Plate I, figure 4 ; 

 and Plate II, figure 5, well illustrate this breaking out or dissolving of the 

 walls between the ed<res in even larger individuals. 



The sculpture consists of " sharp, undulating, transverse striae and 

 scarcely conspicuous' longitudinal ones." (PI. II, tigs. 5 and (>.) The finer 

 longitudinal ribs alone, however, are continuous and the wavy cross-ribs con- 

 nect with them. Although the latter sometimes unite to form continuous and 

 very prominent cross bands, their whole appearance is such as to suggest that 

 they are wrinkles of shrinkage. The undulating transverse and the finer 

 straight longitudinal ribs are so characteristic a feature that they can safely be 

 •used to distinguish this form from Conularhi Trentonensis, Hall, C. Hudsoni, 

 Emmons, and C. quadrat®, Walcott, which have straight and continuous 

 transverse ribs. The undulating transverse ribs are of special importance in 

 the study of the young Conularice, as they are easily recognized by their 

 characteristic form whenever the surface film is sufficiently preserved, 

 however delicate it sometimes may be. 



The cast of the interior often shows, in different parts of the same 

 specimen, either the filling of the transverse ribs as similar ridges, or pustules 

 (cf. PI. I, fig. 1) and deep furrows in place of the longitudinal ribs, or only 

 the latter, or in many places the cast is perfectly smooth. The last fact is 

 accounted for by specimens similar to that represented in Plate I, figure 4. 

 This interesting young Oonularia, which at the distal end shows the straight 

 -ideate edges of a Oonularia, has in the middle part preserved the wall which 

 consists of two layers — an exterior dee}» black, apparently carbonaceous one, 

 which shows the characteristic ribs of C. gracilis, and a much stronger inner 

 layer w hich has a more greyish, mineral appearance and is probably richer in 

 calcium phosphate. This second layer in the middle part between the two 



