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THE AMERICAN NATURALIST [Vol. XLII 



terly meaningless, or again only partly useful, qualitative 

 phrases which may be given. The correlated variability 

 of some of the characters is important. Descriptions 

 based on the mean and range of variation of each char- 

 acter and so expressed are better than those based on 

 values taken here and there at random and then, when 

 once published, petrified into a specific type ideal. A 

 naturalist later tries to identify a specimen with this very 

 limited description, but the characters of the specimen are 

 too divergent and so a new species is created. Still later 

 another naturalist works with a hundred specimens, in- 

 cluding the characters given for the two preceding 

 species, and then synonymy is born and with it trouble 

 forevermore. 



As an illustration of the usefulness of biometry for the 

 solution of taxonomic problems I may take the case of 

 the common Florida-Caribbean holothurian described in 

 1851 by Pourtales as Holothuria ftoridana. In 1868, 

 Semper considered this species identical with H. atra 

 Jager, 1833, from the Celebes. All authors have fol- 

 lowed Semper to the date of my publication (1905). In 

 the meantime Ludwig, in 1883, recognized a species in 

 the West Indies different from the Indo-Pacific form and 

 failing to identify it with //. for id ana Pourtales, created 

 a new species, II. mexicana. The same error was re- 

 peated by Theel, in 1886, in making his H. africana. 



With a feeling that things were not as currently ac- 

 cepted, I concluded to apply the method of biometry to 

 this problem. From the United States National Museum, 

 Harvard University, and my own collections, 138 speci- 

 mens, covering nearly the whole geographical distribu- 

 tion of the two species were available for the work. In 

 the solution of the general problem before me no attempt 

 was made to determine place modes of which, in minor 

 details, there were sometimes indications. Every im- 

 portant character was submitted to statistical study and 

 the result is that H. floridona Pourtales is reestablished 

 as a valid species, with H. mexicana Ludwig and H. 



