NOTICE OF PALEONTOLOGY OF NEW-YORK, VOLUME IV. 157 



MeRISTELLA (MeRISTINA) MARIA. 



Showing the first volution of the spiral lamellae. ' 



The same characters have also been observed with equal distinctness in 

 M. nitida of the Niagara group. In neither of these species is there any 

 indication of accessary lamellae as in Athyris, nor evidence of the exten- 

 sion of the loop beyond the point e; and we are therefore induced to believe 

 that the simple character of the spires in these forms will constitute another 

 distinction, which may conveniently be termed Meristina. 



The Genus Atrypa, as applied to forms strictly congeneric v^iih. Atryya 

 reticularis^ embraces but few species, and these are regarded by some palaeon- 

 tologists as merely varieties of still fewer species. 



In this volume, the Atrypa impressa of the Schoharie grit is continued 

 as a distinct species : although resembling the A. reticularis in general 

 features, it presents a wide departure from the forms of that type in other 

 strata ; and if we are to regard these varieties as due to physical causes, 

 the nature of the sediments, etc., then there is reason to believe that in 

 other instances the same physical influences have produced changes which 

 are recognized without hesitation as of specific value. 



The Atrypa reticularis, in its various phases, occurs in the Corniferous 

 limestone, the Hamilton and Chemung groups. 



The Atrypa spinosa (Hall), or Atrypa aspera ( Schlotheim), is 

 recognized as a very distinct and well-marked species, occurring in the 

 Corniferous limestone, Hamilton and Chemung groups. In the Hamilton 

 group it is more abundant and better preserved than in any other forma- 

 tion ; and occurring in the same beds with A. reticularis, it never approaches 

 that one in character ; there is no difficulty in distinguishing the one 

 from the other ; and the same is true of these forms in the Chemung group. 

 It is also observed that the same distinction between these species exists in 

 Illinois and Iowa. 



The Atrypa hystrix of the Chemung group is likewise regarded as a dis- 

 tinct species, though possessing many features of an extravagant A. spinosa. 



A species of Atrypa, closely resembling the A. marginalis of Dalman, 

 occurs in the Corniferous limestone. This species, Atrypa pseudomarginalis, 

 is of rare occurrence in the rocks of New-York. 



