424 



NEW YORK STATE MUSEUM 



Monograptus from the higher Siluric beds in which Climacograptus is 

 unknown. 1 Hisinger, hence, for practical reasons should be made the author 

 of C . s c a 1 a r i s . 



Tornquist has among other facts shown that in the initial part of 

 the rhabdosome, a " biserial chamber" is found, which after having pro- 

 duced two pairs of regularly alternating thecae, is divided by the median 

 septum into two uniserial canals originating in the common chamber. This 

 difference between the initial and other parts of the rhabdosome is also 

 distinctly shown in the specimens from Maine, by the character of the 

 median suture upon the lateral faces [see text fig. 385], the first two pairs of 

 thecae beino- clearly interlocked or alternating and the straight suture 

 beginning above them. 



The specimens from Maine are preserved only as quartz fillings of 

 the somatic cavities and all periderm is lost. In these fillings the obliquely 

 directed parts of the thecal tubes are much inflated and the initial and distal 

 parts depressed. The result of this is that the rhabdosome appears 

 strongly annulated in its more distal parts, where the thecae have ceased to 

 be alternating and as a rule are placed directly opposite each other. It can 

 hardly be assumed that this feature is entirely due to a much varying thick- 

 ness of the periderm and that the proximal and distal parts of the thecal 

 walls were much thicker than the middle part, for there is nothing seen in 

 the sections of C . scalar is published by Tornquist to indicate an)" such 

 differences in thickness of the periderm. 2 Nor is there any trace of inflation 

 shown in the exterior views of periderms given by Tornquist. 3 His careful 



'Tullberg [1885, p. 5] and Tornquist [1897, p. 6] consider the straight body on the 

 slab as a Climacograptus, probably different from Prionotus scalar is Hisinger. 



2 It must, however, be admitted that the thin sections of Monograptus furnished by 

 Perner show that sometimes considerable differences exist in the thickness of the thecal 

 walls. 



• These inflations have nothing to do with the globular protuberances of C. u 11 d it- 

 1 .1 1 11 s Kun k, which arc " free prolongations of the lower lamina of ea< h thecal partition " 

 that extend downward over the aperture. 



