IQQ REPORT ON THE STATE CABINET. 



backward and bifurcating, to form the accessary lamellae, are continued 

 from their origin obliquely backwards into the cavity of the ventral 

 valve, and, then recurving upon themselves, are reunited laterally; while 

 in Athyris they are intercalated between the first and second turns of 

 the spire, and coalesce with the lamellas of the latter. 



At the same time an examination of the Niagara species referred by 

 me to the Genus Meristella presents a different condition of the interior, 

 and shows the lamellae of the spires united by a simple loop only. 



This feature is illustrated in the accompanying diagram of Meristella 

 (^3£eristinct) maria, Avhich represents a single turn of the spiral lamellae, 



from their origin at a, to i where the bands 

 are cut off. The thickened bases of the 

 crura ai'e represented at a; h is the point of 

 recurvation, c the continuance of the lamellae 

 in the dorsal cavity, and c? the expansion on 

 the inner side into long processes which 

 unite at e, forming the loop. 

 The same characters have also been observed with equal distinctness 

 in if. nitida of the Niagara group. In neither of these species is there 

 any indication of accessary lamellae as in Athyris, nor evidence of the 

 extension of the loop beyond the point e ; and we are therefore induced 

 to believe that the simple character of the sphes in these forms will con- 

 stitute another distinction, which may conveniently be termed Meristina. 



GENUS ATRYPA (Dalmax). 



The Genus Atrypa, as applied to forms strictly congeneric with Atrypa 

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

 palsepntologists 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 ^4. reticularis 'n\ 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 Atryp)a aspera (Schlotheim), is recognized 

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



