114 TERTIARY SPECIES OF PLANORBIS AT STEINHEIM. 



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

 obtuso-costate, but as tliey are both exactly parallel in the production of the distorted varieties, plati/stoinus 

 and difitortus, it was not considered necessary to go to the expense of making up and photogi-aphitig anotlier 

 plate. Fig. 25 PI. S'S, fig- -6 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 tliey show accurately the foi-ms 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 tlie latter. 



