534 Dr. F. A. Bather — The Mount Torlesse Annelid. 



THE STRAIGHT FOEM. (Figs. 1-3.) 



Mr. M'Kay (1881, p. 90) described this as "a tapering tubular 

 calcareous^ body, varying from one to three inches in length, the 

 greater diameter of the larger specimens being not more than 

 a quarter of an inch. In most cases when they occur between the 

 bedding planes of the rock they are found flattened by the pressure 

 of the overlying stratum, but when found vertical or highly inclined 

 to the bedding planes they preserve their cylindrical form. In their 

 fossil condition the walls of the tube are sufficiently thick to have 

 resisted any ordinary amount of pressure exercised by the overlying 

 beds, and therefore it may be doubted if they have always been as 

 calcareous as they now are." Mr. M'Kay believes that the animals 

 " were during life fixed to one place," and that the vertical " is their 

 natural position." 



To the preceding little can be added beyond more precise measure- 

 ments. The greatest length of any of our specimens (No. 24, Fig. la) 

 is 71 mm. (a little less than 3 inches), but this is obviously incomplete, 

 being truncated at the smaller end by a slickensided joint-face, while 

 the larger end has been broken off. At the smaller end, which is 

 much flattened, the mean diameter is (2-3 -\- 14) -^ 2 == 1-85 mm. 

 (=-6\-in-)' -^^ the larger end the mean diameter is (2-9 -f- 1*9) 

 -^ 2 =: 2"4mm. The rate of tapering, therefoi'e, is very slight, and 

 the same is the case in other specimens. Since all the specimens are 

 flattened in the plane of bedding, the lumen appears as little more 

 than a dark line. A section of another individual in No. 24 gives 

 the following measurements : — Greatest diameter, 4-7 mm. Least 

 diameter, 1*3 mm. Greatest width of the compressed lumen, 2*7 mm. 

 Thickness of tube-wall, on one side of lumen, -3 mm. ; on the 

 opposite side, •8 mm.; at one end, 1*3 mm. Probably this last 

 measurement is exaggerated, and the lumen was really longer 

 in this direction. Before compression, therefore, the tube at this 

 level may have bad a diameter of about 3-5 mm. with a wall 

 •8 mm. thick, and a lumen 2*7 wide, or just under four-fifths of 

 the total diameter. These measurements should be checked from 

 individuals preserved in a vertical position, such as unfortunately do 

 not occur in the material under examination ; but assuming their 

 approximate correctness, it can scarcely be maintained that such 

 a tube with its infilling of fine mud ought, however "calcareous," 

 to have resisted the considerable pressure to which it has been 

 submitted — a pressure which the rock-specimens themselves, as well 

 as the published sections of the country, show to have been by 

 no means " ordinary pressure exercised by the overlying beds*" 

 Consequently, there is no reason to suppose that the tube-wall was 

 ever more horny than calcareous. As a matter of fact Mr. M'Kay's 

 argument starts from an erroneous assumption : the substance of the 

 fossil is not a carbonate or any salt of lime, but a chalcedonic form of 



1 Hector (1885, p. 339) also says "a calcareous tubular body." None of the 

 specimens submitted by Mr. Ferrar are calcareous, but all, from all localities, are 

 silicified throughout. 



