CLARK : PLATES IN CRINOIDS 309 



sodium hydroxide solution used in comparing the hydrochloric 

 and sulfuric acids was used, for which the ratio HCl:NaOH was 

 1.0464. The mean of four concordant determinations was 0.9981. 

 Summary and conclusion. The results of the foregoing stand- 

 ardizations are summarized in the following table: 



Summary of Standardizations 



Method 0.1 N factor for HC1 



Direct by Hulett and Bonner 0.9980 



Direct by AgCl 0.9984 



H 2 S0 4 -BaS0 4 -NaOH-HCl 0.9984 



H 2 S0 4 -Na 2 C 2 4 -NaOH-HCl 0.9982 



C 6 H 5 C0 2 H-Ba (OH)s-HCl , 0.9984 



C 6 H 6 C0 2 H-NaOH-HCl * 0.9981 



The close agreement of these results proves the accuracy of 

 the benzoic acid method. Moreover, benzoic acid has many 

 advantages. Its high molecular weight permits the use of large 

 samples, thus reducing the error of weighing; its stability and 

 lack of hydroscopicity make it very convenient; and the method 

 is rapid, since a single weighing and a titration are all the opera- 

 tions involved. These considerations, combined with the ease 

 of obtaining it in a high state of purity, make benzoic acid an 

 excellent material to use as a standard in acidimetry and alka- 

 limetry. 



ZOOLOGY. — The homologies of the so-called anal, and other plates 

 in the pentacrinoid larvce of the free crinoids. Austin Hob art 

 Clark, National Museum. 



In the course of my studies upon the recent crinoids I have 

 been able to examine many hundreds of pentacrinoid larvae 

 belonging to numerous species distributed in several families, and 

 many points hitherto involved in obscurity have been made clear. 



Unfortunately all of the work previously done upon the develop- 

 ing crinoid has been based upon one or other of the species of the 

 genus Antedon, one of the most specialized of the genera in the 

 group to which it belongs, and hence one of the least satisfactory 

 for purposes of phylogenetic investigation. 



