NO. 1117. PROCEEDINGS OF THE NATIONAL MUSEUM. 675 



Bernard writes "that animals closely resembliug Jpus were extaut in earliest 

 times we now know for certain * * * from tlie remarkable Cambrian I'rotocaris 

 VHDshii, which apparently possessed the same pecnliar characters of the posterior 

 segmentation as Ajyiis, and which I should like to call Ajnis marshii."^ 



The fauna in wliicli Protoearis occars in (ieorgia, ^''eI■mont, is entirely 

 marine, and is associated with cbaracteristic Lower Cambrian trilo- 

 bites and bracliiopods. 



GEOLOGICAL HISTORY OF THE APODIDiE. 



Living Apodidie, altliongb rare, are, however, widely distributed over 

 the continents, generally in fresh-water ponds and pools. Three or four 

 days suffice to develop the nau})lius from the egg, which may have lain 

 buried in mud from the previous season. 



Fossil Apodid;e are occasionally discovered in fresh-water Tertiary 

 deposits, and before the true systematic ])osition of Dipeltis and Froto- 

 caris was known, no members of this family were believed to exist earlier 

 than the Triassic. Salter^ mentions a true Apus from the Triassic of 

 Europe. Zittel, in his Handbuch der Paheoutologie, says that Prest- 

 wich described Apus duMus from the Coal Measures of England. From 

 Doctor Charles E. Beecher, the writer learns that '*A. dubius seems to 

 be an abdominal segment or plate of some euryi^terid." In Dipeltis the 

 family is represented in the Upper Carboniferous, and, although the 

 carapace of Frotoearis is not entirely Ai)us-like, there is not much doubt 

 that the genus belongs in the Apodid*. The history of the family 

 therefore, extends throughout the time represented by the entire known 

 fossil- bearing rocks, as Frotocaris occurs at the base of the Lower 

 Cambrian. 



Since the Apodidip, are generally believed to be of late introduction 

 geologically, the family has been regarded as a highly specialized grouj), 

 by Salter and Packard. The latter writes : 



In conclusion, therefore, we consider the Phyllopods as a whole, especially the 

 Apodid;e and Branchipoda^, to be a comparatively recent, highly specialized group, 

 which were developed under exceptional biological conditions in bodies of fresh 

 water, and which, as in Apus, show that this branch of the Crustacean genealogical 

 tree has culminated. The irrelative repetition of the segments and appendages 

 (in Apus) gives evidence that the type, so far from being ancestral, is one compara- 

 tively modern, specialized, and fully worked out. ^' 



In his studies of the Apodid;e, Bernard also recognizes the imper- 

 fection of the geological history of the family, but for reasons given, 

 mainly anatomical, concludes that ^'Apiis is a very ancient form in 

 spite of the deficiency in its own geological record." * In a later 

 pai)er,* he states that Frotocaris marshii might be called Ajms marshii, 

 thus recognizing the great geological age of the Apodida?. 



Frotocaris and Dipeltis inhabited marine waters, while all recent 

 species are denizens of fresh waters, generally of ponds and pools. 



1 Quart. Jour. Geol. Soc. Lond., L, 1894, p. 413. 



■2 Quart. .Tour. Geol. Soc. Loud., XIX, 18(58, pp. 87-92. 



3 Twelfth Ann. Rept. IT. S. Geol. Surv. Terr., Pt. 1, 1883, p. 419. 



^The Apodidie. A morphological study. Nature scries, 1892, p. 182. 



■^ Quart. Jour. Geol. Soc. Lond., L. 1894, p. 413. 



