260 Professor T. Rupert Jones — 



those described and figured in the " Monograph of Fossil EntherioB " 

 (Paleeontographical Society), 1862, pp. 109-111, pi. iv, figs. 8-11. 



1. There are some from the same locality as those already dealt 

 with, namely, Eslheria Forbesii, Jones, from Cacheuta in the 

 province of Mendoza, Argentine Kepublic. 



2. Others collected by David Forbes at another place, namely, 

 Arica,' Department of Arequipa, in Southern Peru. 



3. An interesting series from Brazil ; partly described and 

 illustrated in the Geological Magazine for May, 1897, pp. 195- 

 202, PI. VIII. 



From Cacheuta and Challao (both in the province of Mendoza) 

 more or less similar specimens have been described by H. B. Geinitz 

 and E. A. Philippi ; and the latter has treated of a species, probably 

 from the district of Lebu, Chili, like that which Dr. Forbes found 

 at Arica. These, therefore, have to be compared. The Brazilian 

 specimens referred to above belong to four new species, including 

 three of JSstheri'ina, gen. nov., elsewhere described. 



The close similarity that many Estherice have one to another 

 in the shape of the carapace, the only part of the animal remaining, 

 when fossil, for the geologist to examine, makes the determination 

 of fossil species very difficult. The limbs and soft parts having 

 perished, the features of the valves, such as shape and contour, 

 the lines of growth and their interstices, are all that give the means 

 of judging specific differences. In the more or less crushed or 

 otherwise modified state in which the fossil carapaces often occur 

 the difficulties are multiplied. 



The sex of individuals influences the carapace ; and the succes- 

 sional stages of growth are accompanied by differences of outline. 

 Many such modifications and variations of form are recognizable 

 in published works treating of these Phyllopods. For example, 

 G. 0. Sars, of Christiania, has well illustrated and explained the 

 gradational changes, from the egg to the adult form, in Cyclestheria 

 Hislopi ^ and Estheiia PackardiJ^ 



§ II. Geinitz, 1876. 



In 1876 Professor Dr. H. B. Geinitz described and figured several 

 fossil EstliericB from the Rh^tic carbonaceous shales and associated 

 dark-grey clays of Challao and elsewhere in the Mendoza province, 

 Argentine Eepublic. All these specimens he referred to Estheria 

 Mangaliensis, Jones : see " Beitriige zur Geologic und Palaeontologie 

 des Argentinischen Republik," 11, Palaeontologischer Theil, 

 Abth. 2; " Ueber Ehaetische Pflanzen- und Thier-Eeste in den 

 Argentinischen Provinzen La Eioja, San Juan, und Mendoza," 

 1876, p. 3, pi. i, figs. 1-6. 



1 Now held by the Chilians as an indemnity for war expenses, or taken by them 

 in 1886. 



2 Christiania Vidensk.-Selsk. Forhandl. 1887, No. 1. 



3 Archiv Math, og Naturv. Atteude Bind, Forste Hefte, June, 1896, Kristiania. 

 In this memoir on £. Fackardi is given the complete history of the growth of an 

 Ustheria and its valves. 



