114 TERTIARY SPECIES OF PLANORBIS AT STEINHEIM. 



Figs. 25-28, first sub-series includes as previously mentioned p. 65, two sub-series, the acuto-oostate and the 

 obtuso-costate, but as they are both exactly parallel in the production of the distorted varieties, platystomus 

 and distortus, it was not considered necessary to go to the expense of making up and photographing another 

 plate. Fig. 25 PL ££, fig- 26 PL costatus, the costae are coarser in these figures than in the specimens and 

 so also are those of PL costatus var. distortus, figs. 27, 28, but they show accurately the forms of this sub- 

 series. 



Note. These plates are described in the text as having been photographed by Sonrel and Black, but the 

 negatives prepared by them could not be used by the Heliotype Company, and the whole were successfully 

 rephotographed by the latter. 



