Vol. 70.] THROUGH THE ANDES OF PERU AND BOLIVIA. 37 



.a group of Eupliemiis urii Flem., 1 in which there are numerous 

 columellar folds projecting more or less widely in front of the 

 mouth; and a group of JEu. orhignyanus Portl., with much less 

 numerous folds, which do not project so far. The latter group is 

 abundantly represented in the Permian of the Salt Range, and 

 also in the Pennsylvanian of the United States. Waagen further 

 suggests a tendency towards diminution in the number of folds 

 concurrently with increased development. 



A well-marked species occurs abundantly in the limestones of the 

 Titicaca district, winch in general form shows a certain resemblance 

 to JEu. indicus of Waagen. 2 In size, however, it is somewhat 

 smaller, and the spiral folds, which are acute and separated by flat 

 furrows, are slightly more numerous than in Waagen "s species, num- 

 bering usually ten in an adult shell. In the young shell they are 

 still more numerous ; but, as one or two die out before the rest, 

 there is a diminution in number with increased growth. Thus the 

 stages of ontogenetic development appear to indicate the phylogeny 

 suggested by Waagen. 



(d) The Devonian Rocks of the Altaplanicie. 



The strongly-marked fault at Coniri, which cuts off the eastward- 

 dipping conglomerates and sandstones mentioned above (p. 29), 

 is bounded on the east by vertical shales, with a strike trending 

 almost due north, succeeded by strongly-folded olive-green quartzites 

 and 3'ellow sandstones with occasional calcareous bands. These beds 

 crop out in a series of rounded hills, alternating with broad alluvial 

 plains, as far as Yiacha, and can be traced far to the north 

 through the district of Tiahuanacu to Archacachi. 



Although no palseontological evidence was obtained, they w T ere 

 ■coloured by A. d'Orbigny and Forbes as Devonian, wiiile Pissis 

 regarded them as of Carboniferous age. That the former determin- 

 ation is correct is now shown by the discovery of Devonian fossils 

 near the village of Coniri. With the exception of this one locality, 

 the rocks appear to be, as a general rule, extremely unfossiliferous, 

 though rolled specimens of a Pliacops of latifrons type are not 

 infrequently found among the alluvial pebbles of the plains. 



Of recent years the Devonian fauna of Bolivia has been studied 

 in some detail by various authors, including Steinmann & Ulrich 

 (1892), Kayser (1897), Ivor Thomas (1905), and Knod (1908). 

 The combined results obtained by these authors show that the rocks 

 of this formation can be correlated with the Lower Devonian of 

 North America, being divisible into two main groups : — an upper 

 or Humapampa Sandstone, corresponding to the Hamilton Group ; 



1 Mr. H. Bolton has recorded Euphemus urii from the basement-beds of 

 the Bristol Coalfield, Q. J. G. S. vol. lxiii (1907) p. 463, and from the Lower 

 Coal Measures of Vobster, ibid. vol. Ixvii (1911) p. 338. It has also been 

 described from the oil- shales of the Lothians, Mem. Geol. Surv. Scotl. 2nd ed. 

 (1912) pi. i, fig. 4. 



2 Pal. Indica, ser. 13, vol. i (1887) pi. xv ; fig. 2. 



