HISTOEY OF RESEARCH. cxlv 



(e) Sicula not exceeding 2 mm. in length ; rhabdosome slender, distally 

 straight, or irregularly bent. M. incommodus, n. s. 



b. Thecas dimorphous : tlie distal ones of the same type as that characteristic 

 of the preceding section, each of the proximal thecas wholly, or at least distally, 

 free from the succeeding theca. 



(a) Rhabdosome gradually widening. M. revolutus var. austerus, nov.,. 



M. difformis, n. s., M. cf. cyphus. 



(b) Rhabdosome abruptly acquiring its normal width. M. limatidus. 



c. All the thecas of the same type ; each being wholly, or at least distally, free 

 from the theca next in advance. 



(a) Rhabdosome stout and straight, or only having the sicular portion 



bent backward. M. runcinatiis, M. priodon, M. SedgwicMi, M* 

 harpago, n. s. 



(b) Rhabdosome slender, proximally arcuate, but not enrolled, distally 



straight or irregularly bent. M . elongatus, n. s. 



(c) Proximal portion of the rhabdosome forming a more or less complete 



flat or sub-conical spiral, or at least showing a tendency to form 

 such a figure ; prolific side convex. M. denticulatus, n. s., M* 

 fimbriatus, M. triangalatus, M. nobilis, n. s., M. decipiens, n. s., M. 

 convolutus, M. subconicus. 



(d) Rhabdosome coiled up in an elongated conical helix bearing thecas on 



the convex margin. M. turriculatus. 



(e) Rhabdosome enrolled in a conical spiral-bearing theca on the concave 



margin. M. proteus. 



(f) Rhabdosome forming a narrow flat spiral, bearing thecas on the 

 concave margin. M. discus. 



(g) Rhabdosome fish-hook-shaped; prolific side concave. M. exiguus. 

 Tornquist points out that he does not imagine that the above arrange- 

 ment is " in every respect a natural one, though he is of opinion that several of the 

 sub-divisions may be found to coincide with true natural groups." 



1899. 

 Tomquist, j n a ghort stratigraphical paper published the same year, 



"Nigra anteckningar Tornquist noticed the various localities where the Upper 



., . , ~ Silurian Graptolitic zones are recognisable in Vestrogoth- 



ofversilunska Urapto- L ° ° 



litskiffrar," ' Geol. lancl - 



Foren. F6rh.,'bd. 21. 



1899. 



Hall, T. S., j n -^ggg jj a ^ p^iig^e^ a general account of the Grrapto- 



• ^ / aP £ Tr- i. lite-bearine' beds of Victoria, and their divisions, comparing 



mg Kocks of Victoria, & r o 



Australia," 'GeoLMag.,' them with those of Europe, 

 dec. 4, vol. vi, no. x. 



u 



