NO. 2 MIDDLE CAMBRIAN HOLOTHURIANS AND MEDUSvE 49 



the material now available it is not perfectl}' clear how many of the 

 " peltato-digitate " tentacles originally existed. Two only have thus 

 far been seen on each of several beautifully preserved specimens. 

 It may be that five will be found, two of which will be fully developed 

 and three immature or atrophied. 



The constriction indicating- the oesophagus is present in many speci- 

 mens. In fact, the canal always narrows at this point even though 

 the oral chamber is not expanded in front of it. The elongated 

 constriction of the oesophagus is well shown by text fig. 5. 



The stomach is the prominent and best preserved part of the 

 animal. It occupies the largest part of the alimentary canal and 

 appears to have had strong, more or less corrugated walls, and in- 

 variably to contain traces of the food in it at the time of the animal's 

 death. This is shown by nearly all of the figures on plates 8-12. 

 The length of the stomach is indicated by figs, i and 4, pi. 9 ; fig. 2, 

 pi. 10; and figs. I and 2, pi. 12. Side views of the compressed 

 stomach are shown by fig. 3, pi. 9; and figs, i and 2, pi. 11. 



The strong walls of the stomach are indicated by fig. 2, pi. 10, also 

 by the fact of its preservation when the remaining portions of the 

 animal have disappeared. Upward of two hundred specimens, in 

 various conditions of preservation, were found in the collections of 

 19 10, and in all of these the stomach was clearly defined. In the 

 simplest form only the outline of the stomach was preserved (fig. 3, 

 pi. 10; and figs. I and 2, pi. 12), but there are all the gradations be- 

 tween this and instances where nearly the entire animal is preserved 

 (fig. 3, pi. 8; and fig. 5, pi. 9). 



The posterior end of the stomach is located where the alimentary 

 canal usually contracts abruptly in size and the shiny area of the 

 stomach terminates. This is illustrated very definitely by fig. 2, pi. 

 10 ; also by figs, i and 4, pi. 9 ; and figs, i and 2, pi. 12. 



The intestine is usually as long as and less than one-half the diam- 

 eter of the stomach. In some examples the canal shows traces of 

 matter inside of it (pi. 9, fig. i ; and pi. 10, fig. 2). The intestine 

 contracts at its posterior end (pi. 12, figs, i and 2), but as yet the 

 actual anal aperture has not been observed. 



Genital organs. — The only suggestion of a genital organ is shown 

 on fig. 5, pi. 9, at (g) where a three-lobed body is pressed in with 

 the subumbrella surface. 



Dimensions. — The largest specimen is represented by fig. 3, pi. 12. 

 The right and left sides have been partly folded under and lost, but 

 by taking the average width of the lobed umbrella outside of the 



