INVERTEBRATES. 



197 



Pig. 10. 



The annexed cut will show the structure of 

 one of these simple rays in /S. sculj)tus,= 

 (Act. sculptus, Hall). Of their entire length 

 we cannot speak positively, as they are in- 

 complete in all the specimens we have seen. 

 In one instance, however, one of them is seen 

 to extend 1.53 inches from the body, or nearly 

 three times the breadth across the body below 

 the rays, at which point it is broken off. 

 Where the pieces covering these arm-like rays 

 have been removed, the cavity within is seen 

 steganocrinus scuiptus. to be very slender, and slightly flexuous at 

 pStofontof fh!rayI(D)! the points where the true arms are given off, 



with the arm-base on each ,i , i r> . i ■ • -< 



side; o represents a part of exactly as in the rays ot the typical species 



the free ray, with its arm- ri n 7 n n 



bases and covering plates, £, pentaqonus, as seen m tig. a, ot cut 9, on the 



as seen in a side view; and ■*■ " J ° ' ' 



Lc?on e of 1 t t L a sa t m a e° ,verse opposite page. As much as they resemble arms, 

 we can but regard them as really extraordinary extensions of the 

 body, and the little tentacle-bearing appendages on each side 

 as the true arms. 



In some instances the first brachial piece, at the base #f the 

 first true arm in S. scuiptus, is larger in one of the rays, than 

 represented in the annexed cut, and presents somewhat the ap- 

 pearance of their being a bifurcation on the third radial, but it 

 is easy to see that there is not a true bifurcation, but that the 

 radial series continue directly on, giving off arms alternately 

 on each side. Of course Prof. Hall was mistaken in describing 

 this species as having only three arms to each ray. 



The vault in the known species of this type terminates in a 

 subcentral proboscis, and the visceral cavity is provided (at 

 least in the typical species (A. pentagonus of Hall), with a spiral 

 Bulla-like organ, as in other types of the Actinocrinidce. 



Of course we do not expect those palaeontologists who insist "upon including 

 in the same genus all the species of crinoids that agree in the number and 

 arrangement of the pieces composing the body, without regard to the most 



