172 



Dr. H. RaufF on the Genus Hindia^ Dune. 



or amputated cylindrical stump is then recognizaLle, wliile the 

 fourth is very seldom observed, and, in fact, appears generally 



Fi- 1. 



to be rudimentary or entirely deficient. It may be remarked, 

 however, that it has several times been recognized with 

 certainty. 



The two distinct rays present a very characteristic form ; 

 they are curved in the same direction, the concave margin 

 always appears smooth, the convex one always toothed, and 

 each of the extremities of the arms (heads), which are widened 

 in a direction about perpendicular to the arm, and lie in the 

 same surface of the canal-wall with the arm, are also toothed 

 on the outer margin. As all the radial sections appear to be 

 equivalent, i. e. furnish tlie same images, we are justified in 

 assuming that the third arm also has the same structure as the 

 two just mentioned, and that the diagrammatic representation 

 in fig. 1 (the shaded part) may represent the Hindia ele- 

 ment *. 



These individual elements are united to one another in a 

 remarkable manner. When the connexion of the skeleton is 

 preserved in tlie preparation, we see, as in the diagram fig. 2 

 (p. 174), radially directed rows of meshes, of which we can 

 usually determine two or three neighbouring ones as belonging 



* Tangential sections, indeed, show three arms distinctly, but, for 

 reasons whicli will appear hereafter, these do not allow the apecitic peculi- 

 arities of the //mrf/rt- element to stand out clearly ; as we examine them 

 from above they appear straight, not curved, and without allowing the 

 dilatations of the heady, the denticulation of the convex sides of the arms, 

 and the peculiar mode of connexion of the latter to be recognized clearl}' 

 and as the rule. 



