104 The Ottawa Naturalist. [Dec. 



cap of a small vial, and the specimen attached to a slide is in- 

 verted over it. This slide is supported by a block or bunch of 

 slides at one end, and a weight placed upon it to hold it in posi- 

 tion. After making the proper adjustments the slide is re- 

 moved, specimen and cover glass treated as before, and the 

 specimen then returned to its inverted position. Gum may 

 now be added from time to time until the gummed area is sufh- 

 ciently large. 



Porous specimens, such as colonies of bryozoa, are best 

 treated by slowly lowering them into a very small volume of 

 the thinner gum solution, thus driving out most of the air. 



If it is desired subsequently to shift the position or angle 

 of the cover glass, it is only necessary to add a little fresh gum 

 at the edges and slowly push the cover to the new position. 

 Deep Petrie or covered cylindrical glass dishes will be found 

 useful in housing the mounted specimens and keeping them 

 from dust. 



To clean : place in benzol until the gum is dissolved. Rinse 

 with a Httle clear benzol and let dry. The benzol used for dis- 

 solving and rinsing may be saved for subsequent operations. 



The plate accompanying this article is introduced to show 

 the value of the process where penetration of recent organic 

 material is desired. The remains of muscle fibers here shown 

 are, in appearance, practically as they appear in many fossil 

 forms, when revealed by the gum process. Note that the first 

 (upper) ambulacral (jaw piece) is supported by a process 

 arising from, the second. The oral end of each ambulacral is 

 firmly attached to the adam.bulacral in advance of it. Between 

 the lowest adambulacral in the figure and the ambulacral at the 

 left of it, there is a dark spot revealing a bit of the buried am- 

 bulacro-adambulacral mtiscle. A contraction of this muscle 

 served to draw the following ambulacral orad. The aborad 

 wings on the oral ends of the ambulacra are so shaped as to 

 allow this motion. While the ambulacra themselves are not 

 truly imbricated, the pairs (adambulacral and following ambul- 

 acral) are distinctly so placed. The numbers on the lower edge 

 of stereogram are those of the original negatives. 



References. 



1911. — Hudson, G. H. Studies of some early Siluric Pelmato- 

 zoa. New York State Museum, Btdletin 149. 



1913 (a).— Hudson, G. H. The use of the Stereogram in Paleo- 

 biology. New York State Museum, Bulletin 164. 



1913 (5).— Hudson, G. H. Does the type of Protopalaeaster 

 narrawayi present an Oral or Aboral Aspect? The 

 Ottawa Naturalist, Vol. XXVII (Oct. 1913) plates 

 VIII-IX. 



