GRAPTOLITES OF NEW YORK, PART 2 47 J 



here retaining - their original recurving direction. Also these triangular 

 extensions become thinner and thinner and finally fade towards the outer 

 margin. 



The much discussed " reproductive sacs," figured by Hall [see text fig. 

 458-61], have now exactly the triangular form of these peridermal exten- 

 sions ; they are bounded on both sides by the same diverging fibers and 

 fade at their distal ends exactly as the latter. Since, however, the bound- 

 ing fibers have lost their connection with the corresponding fibers of the 

 preceding thecae, the triangular extensions have changed their original 

 recurving direction into a horizontal one and appear now as free appendages 

 suggesting vesicles or sacs which have opened distally [see pi. 29, fig. 16 ; 

 pi. 30, fig. 3, 8]. Still, even with the distal ends free, they frequently 

 retain more or less of their original recurving position, as in plate 30, 

 figure 3. 



On the base of these observations we consider the " reproductive sacs " 

 of Lasiograptus as flat, horizontal extensions of the periderm of the lower 

 apertaral margins of the thecae between the bases of the apcrtural loops. 



There are other observations supporting this view. In the best pre- 

 served appendages a system of cross-fibers can be seen to connect the 

 bounding main fibers [see pi. 30, fig. 8] and in others these are seen to be 

 again connected by finer fibers, the whole forming a fine meshwork. In 

 others [see especially pi. 30, fig. 1] the bases of the main fibers are con- 

 nected by a system of fine longitudinal fibers running parallel to the axis 

 of the rhabdosome, and these again form together with transverse fibers 

 a meshwork, that must have screened the vertical sides of the spaces 

 formed by the horizontal apertural extensions described above. The result 

 were prolongations of the thecae, amounting to twice and more of their 

 length as given by the continuous periderm. I have tried to illustrate the 

 structure of these extended thecae as I derive it from my material, in 

 diagram plate 31, figure 5. The similarity between this thecal structure 

 and that of the later Stomatograptus is very pronounced. The final aper- 

 ture lay between the recurving parts of the two main fibers above the point 



