1881,] NATURAL SCIENCES OF PHILADELPHIA. i^09 



the convolutions are directed outward from left to right, varying 

 in number from two to four in different species. 



In the usual state of preservation the walls are perfectly solid, 

 almost like a " convoluted plate " as which it was described by 

 Hall. In transverse sections, they are seen to be strong, and 

 appear to be constructed of two partitions closely fitted together 

 and united at the edges. The unusual thickness and apparent 

 double natui'e of the walls in these specimens misled Wachsmuth 

 in 1877, who considered the walls to be the body of the alimentary 

 canal. This is evidentl}- a mistake. We now know, from a num- 

 ber of other specimens, that the wall was simple in all cases, very 

 delicate, and constructed of an extremely fine filigree work, which 

 generally in the fossil became thickly incrusted with silicious 

 matter on both sides, thus producing the apparent duplication of 

 the wall. In good specimens, a magnifier fWiows the wall to be 

 composed of an extremely fine network of minute pieces or bars, 

 with intervening meshes. These bars, according to Meek and 

 Worthen, " do not intersect each other at anj- uniform angle', but 

 anastomose so as to impart a kind of irregular regularity to the 

 form and size of the meshes." 



That this network was in some wa}' connected with the diges- 

 tive organs, is no doubt true, but whether it formed a mere sup- 

 port for the digestiA^e sac, as Meek and Worthen suggested, or 

 was an extensive plexus of blood vessels surrounding the ambu- 

 lacral canal, is a question we are as yet unable to solve. It should, 

 however, receive a more appropriate name than any yet given, and 

 we propose to call it the " oesophageal network," which may be 

 changed when its special functions and aflftnities are discovered. 



One of the writers found a specimen of Actinocrinus, in which 

 the convolutions were nearly intact, and b}'^ removing the outer 

 fold, the inner or upper end, as distinguished from the outer or 

 terminal part, could be examined (PI. XIX, fig. 12). The organ 

 has the usual dense structure, and where it comes into view, is an 

 elongate tube, which passing downward widens at first gradually 

 to near the middle of the visceral cavity, then rapidlj^ until it 

 attains a width equal to two-thirds the entire length of the cavity. 

 The upper part descending spirally turns from right to left, but 

 on becoming wider the whorls are abruptly reversed , and there- 

 after the convolutions are from left to right. The outer end also 

 tapers rapidly, assuming the form of a flattened tube, and ascends 



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