174 NEW YORK STATE MUSEUM 



strikingly similar to those found on the ventral side of any 

 S c u t el 1 a. 



The opposite or dorsal side likewise gives evidence of 

 these structural channels. I am satisfied however, that these 

 do not appertain to this surface but have been developed 

 in such specimens by compression against the ventral sur- 

 face; for where these channels are most strongly developed 

 they correspond in shape and position on the two sides, as is 

 seen by laying one side on the other, as it was when they were 

 found in the rock; furthermore, specimens which have been some- 

 what obliquely compressed, or lodged in the matrix at such an 

 angle that compression failed to bring the opposiite faces into 

 contact do not bear these markings. The leading character of 

 this dorsal surface, however, consists of a great number of 

 radial lines departing from the central point of the disk. We 

 observe, first, that these radial lines about the center have some- 

 what the appearance of broad cords closely knotted at regular 

 intervals. We may conceive of two such knotted cords lying 

 side by side, the knots of one fitting into the intervals of the 

 other, each pair very gradually widening outw^ard from the 

 center and each separated from the next pair by a smooth, ligu- 

 late area not wider than the cords. Or these radii may be 

 likened to a series of braids widening outward. The number of 

 such braids meeting at or departing from the center has not been 

 definitely determined, as in the most complete of the specimens 

 they are not suflSciently distinct to permit enumeration. They 

 are, however, very numerous. Where most clearly retained there 

 are about 25 in approximately one half of the surface. Probably 

 it would not be an overstatement to place at 50 the number of 

 these radial braids actually departing from the center of the 

 disk. 



These radial bands are, however, simple for only a part of 

 the radial length. At a point considerably within one half of 

 the radius of the disk each tapers to a definite extremity. In 

 other words, the smooth intervening arfeas bifurcate and the 

 branches of each join with the branches at their side. Thus by 

 the branching and inosculating of the intercalary areas the 



