100 



PALEONTOLOGY OF NEW YORK. 



more naturally rest in association with Seminula subtilita than with the group 

 of Spirigerella Derbyi. 



We have no satisfactory evidence of the occurrence of Spirigerella in 

 North American faunas. 



The type of structure characterizing Athyris is continued beyond the 

 PalaBOzoic, being abundantly represented in the Alpine Trias faunas. These 

 later fossils have been studied by various authors, and most recently de- 

 scribed by BiTTNER,* who has subdivided them into a number of groups all of 

 which he holds subordinate in generic value to Spirigera ( = Athyris). Of 

 these, two principal divisions are made : 

 (I) Forms with simple spirals ; 

 (II) Forms with double spiral bands. 

 Of the former are : 



1. The "genuine Spirigeras"; under which are included: 

 a. Smooth forms. 



h. Species with sloping shoulders', retzioid rather than athyroid in out- 

 line, and bearing on the surface a few sharp plications, which, at 

 the margin, are opposite, not alternate ; Pliciqera. 



KIO. 74. Fio. 76. 



FlR. 74. TetractineUa trigoneOa. Scblothoim. 



Fig. 75. Loop oi' IHoristelld ivdUtincta, lleyrich. 



Fig. 76. AmfkUomella hemitpharoidica, Klipstein. 



KIG. 7«. 



(BITTNBB.) 



* BrachioiMMlen tier Alpinen Tiias: Ahhandl. der k. k. geoUig. Reichsanst., Bnd. xiv. 1890. 



