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POPULAR SCIENCE REVIEW. 
Figs. 25, 26, and 27 give diagrammatic but correct transverse sectional 
views of common forms of Acanthometrine spines, in order to 
show the ribbed or flange-like structure which engenders the 
appearance of tubularity in these spines, in consequence of the 
rib or flange-like portion extending longitudinally along the 
centre of the spines. 
„ 28, 28 a, and 28 b are diagrammatic representations of the truncate 
Acanthometrine spines, presenting the split appearance, 28 b 
showing the split when the object is not viewed under a 
sufficiently high magnifying power, in a suitable medium, or 
under imperfect illumination. Fig. 28 shows the same, when 
proper definition is secured. 
