GRAPTOLITES OF NEW YORK, PARY 2 47 1 



other features, mainly the position of the apertures ; Retiolites having its 

 thecal apertures parallel to the main axis and the other having them 

 inclined [see text fig. 454] ; and that in Retiolites the parietal and* mouth 

 ledges are notably thicker than the mesh fibers and in Stomatograptus the)' 

 are not. In these and other characters our form is a typical Retiolites. 

 Since, moreover, the other and more complete specimen fails to show like 

 circular depressions, it is to be inferred that those of the smaller specimen 

 represent rather an accidental feature of preservation than one of original 

 structure. 



I seriously doubt the specific difference of the American form 

 from R . geinitzianus, the genotype of Retiolites ; for not only are 

 the two exactly alike in dimensions and habit, but they tally also com- 

 pletely in the number of thecae within 10 mm and in their inclination, as 

 a comparison of my material with Tullberg's [1883] careful drawings 

 and the descriptions of others has clearly shown. Since, moreover, R . 

 venosusis associated with Monograptus clintonensis, which is 

 but little different from M . p r i o d o n , and the latter and R . geinitz- 

 ianus are associated in the middle Siluric of Europe, to the lower part 

 of which our Clinton beds correspond, also the horizon and association of 

 our form are suggestive of its identity with R . geinitzianus. 1 



We have for these reasons, for the present brought R . venosus as 

 a variety under geinitzianus, allowing this distinction to stand less 

 by virtue of differential characters than by that of different geographical 

 distribution. But when the wide areal distribution of R . g e i n i t z- 

 ianus in Europe (Bohemia, Carinthia, Saxony, Silesia, France, England 

 and Scandinavia) indicating its occurrence in several basins is taken note of, 

 the wide geographical separation of the American and European forms also 

 loses much of its importance. 



1 Freeh lias inferred from Hall's figures that it differs from R . geinitzianus in 

 the shorter length of the apertural mucros, but since the latter are but the result of the 

 doubling upon themselves of the mouth ledges and in reality no mucros, this difference 

 can be only one of preservation. 



