clviii BRITISH GRAPTOLITES. 



mid free region, having a mouth at its outer extremity. Thus the stipe in Rhabdo- 

 pleura presents an appearance similar to that in some forms of the Monograptidse 

 (especially Rastrites) ; the longitudinal tube in Rhabdopleura answering in form and 

 relation to the common canal in Rastrites, and the free portions of the successive 

 chambers to the so-called " isolate thecas " in that genus. In Rastrites, however, 

 while the successive thecas intercommunicate freely by means of the common 

 longitudinal canal, in Rhabdopleura they intercommunicate only in their earliest 

 stages, and later on in life are completely shut off from each other. 



Imbedded in the dorsal wall of the longitudinal tube in Rhabdopleura, there 

 runs from end to end an intensely black filament or cord, denominated by Schepo- 

 tieff as the stolo (a title which we here retain in this place for convenience of 

 reference). This stolo is composed of four members, namely, (1) an exceedingly 

 minute axial rod running continuously down its centre and surrounded by three 

 concentric tubular structures, (2) an inner cell-string, (3) a middle branching 

 cell-layer, and (4) an outer cover of intense blackness. 



Schepotieff agrees emphatically with those of his predecessors who have 

 pointed out the agreement in position and relation of this stolo in Rhabdopleura 

 with the virgula in the Monograptidas, and he fortifies his view by the results of 

 his own microscopic studies and those of others into the structure of Monograptits. 

 He also brings forward other points of similarity in structural detail between 

 Rhabdopleura and Monograptus, etc., such as the common presence of minute 

 growth-lines or transverse rings which meet at an angle on the ventral side of the 

 thecas, the presence of periodic projections on the solid axis, etc. 



We are wholly unable to agree with Schepotieff 's identification of the growing 

 portion in Rhabdopleura with the sicula in Monograptus, but his paper (which 

 is illustrated by several good Text-figures) should be read by all students of 

 Graptolite literature. 



,„„„ In a first of these notes the author expresses his agree- 



1906. . . 



m-. . . o r ment with the views of those who regard the Dictuonema 



l urnqui&t, a. h., » 



" Sundrv Geological and Geratopyge beds of Sweden as constituting in combina- 



and Palseontological tion the first member of the Scandinavian Ordovician. In a 



Notes," 'Geol. Foren. second he discusses at length the synonomy of the forms which 



have been referred to Isoqraptus qibberulus (Nich.), B'uhimo- 

 pp. 497-515. J i J v /' J 



g rapt us pa talus (Hall), and Didi/mograptus constrictus (Hall). 

 1906. A comprehensive essay on the Dictyonema and Geratopyge 



Moberg, J. C, and beds of Sweden, regarded as constituting collectively a single 



Segerberg, C. 0., formation. This is divided by the authors into two main 



"Bidrastillkanndomen i , U. , , ,• n 



sections, namely, a lower or Victyoqraptus section, and an 

 om Ceratopvgeregio- , ' ' 



nen " ' Lund's Geol upper or Geratopyge section, each of these sections being 



Faltklubb.,' ser. b, composed of a lower and an upper zone. All the fossil forms 



no. 2, pp. 1-110, — Brachiopoda, Trilobites, and Graptolites — recognised by 



P ls ] v " the authors as afforded by the formation, are figured and 



