Dr. F. A. Bather — Studies in Edrioasteroidea. 259 



PLATE X. 



mlcrophotographs of grains of heavy detrital minerals from 

 the Suffolk Box-stones. 



Fig. 1. Angular grains of pink garnet. Mouth of E. Deben. [203.] Seep. 254. 

 ,, 2. Andalusite, Sutton [206], many grains dusky with inclusions. 



See p. 255. 

 ,, 3. Epidote, Sutton. [206.] The darker grains in the photograph are 



those giving the strong yellow-green tint due to pleochroism. 



See p. 255. 

 ,, 4. Staurolite, Foxhall. [202.] Irregular angular grains, a few showing 



frayed edges. See p. 255. 



III. — Studies in Edrioasteroidea, VII. Morphology and Bionomics 

 of the Edrioasteridae. 1 



By F. A. Bather, M.A., D.Se., F.B.S. 



Published by permission of the Trustees of the British Museum. 



THE facts concerning the Curvature of the Subvective Grooves have 

 been summarized in Study IV (1914, p. 122). They show that 

 no distinction can be drawn in this respect between Edrioasteroidea 

 and Cystidea Diploporita, as some have pretended. 



The facts of individual growth, as inferred from a comparison of 

 large and small specimens of the same species, indicate that the rays 

 increased in relative length with age, and thus wound more and more 

 along the periphery. It may further be inferred, from tracing the 

 course of each ray, that the initiation of the curve was due simply to 

 the primitively straight course of the ray being turned aside by the 

 peripheral limit. It follows from this that the right-handedness or 

 left-handedness of the coil was not a feature of the young, and that 

 the one is not a mere reversal or mirror-image of the other. The 

 distinction, however, being characteristic of species separated by other 

 characters, cannot be fortuitous. There must have been some 

 structure or habit in each species predisposing a turn of the coil in 

 a solar or contrasolar direction. It is clear that the cause cannot 

 have been, as Jaekel seems to suggest (1899> p. 24), a torsion of the 

 circumoral region, for in that event the proximal and distal curvatures 

 of a single groove would never be opposed, as they so often are, and 

 that not only in the right posterior ray. 



If the difference of coil were due to such a fundamental change in 

 the constitution of the animal as would produce a mirror-image, then 

 the change would be accompanied by a change in the coil of the 

 gut from solar to contrasolar or vice versa. This, however, does not 

 seem to have been the case, for such evidence as we have as to the 

 position of the rectum indicates a solar coil (as viewed from the oral 

 pole) whether the grooves were solar as in E. buchianus (Study II, 

 1900, p. 199) or contrasolar as in E. Ugsbyi (Study IV, 1914, p. 167). 

 Jaekel's conclusion that the gut of the Edrioasteroidea had the normal 

 solar coil of Echinoderma is probably correct, though his main 

 argument, drawn from the supposed constant contrasolar curve of the 

 rays, rests on an incorrect premiss. 



1 Continued from p. 215. 



