112 HYATT ON THE TERTIARY SPECIES 



Line d, figs. 1-7 PI. crescens. Fig. 2 line d sliows a specimen of the young, wliic.li at a very early age 

 begins to show the compressed form of the whorl, which distinguishes the adult of PI. crescens. In feet the 

 three young specimens on this line form a series in this respect, fig. 2 being the most compressed, fig. 6 next, 

 and fig. 4 tlie least, although figs. 2 and 4 are of the same age and fig. 6 a little older. The adults of all of 

 the three would have been about equally compressed in form. 



Plate VI. 



Magnified 5>3 diameters. 



Line n, figs. 1-3 PL letns from Undorf, 4-7 PL '""■'HvS;" {=revertetis Hilg.). 



Line b, figs 1-6 PI. '"'"^,'^'" {^reverteiis Hilg.), somewhat stouter than the normal forms of PI. lens, even 

 in the young, fig. 5. 



Line c, figs. 1-5 PL ox)/stoinus with extremely stout whorls even in the young. In tliis variety the young 

 are very similar to the rotundatiis-like young of PL trochiformis, see pi. 2, line o, figs. 1-14, line p, figs. 1-8. 

 They, however, are distinct in the aspect of the upper umbilicus, in the carinatious and shell, and outline of 

 tlie opening of the whorl, especially in the younger stages. Compare also figures on lines o and p, pi. 3, with 

 figures of young of PL oxystoinus var. coc/deatiis, pi. 3, line 1, figs. 4-11, w^hich also have extremely stout 

 whorls in the young. Fig. 6 is. a fine specimen of the transition from the normal variety- to the turretted 

 form, variety cor.hleatus of PL oxystoitms.^ 



Line d, fig. 1 PL oxt/stomus var. cochleatus. full grown shell," figs. 2-4 PL oxystomus, normal vnriety, 

 showing the identity of a young shell, fig. 4, with a shell of the same size of PL levis, from Undorf. 



Line e, fig. 1 PL supremus var. turritus, figs. 2-4 PL supremus. 



Plate VIL^ 



Magnified 4 diameters. • 



Line a, figs. 1-2 PL Icvis, Undorf. Figs. 3-5 are deeply umbilicated forms of PL Steinheimensis which 

 are similar to fig. 1 in this respect and in the form of the whorls. Fig. 6, PL I'vis, Undorf, to compare with 

 figs. 7-9 PL iSteinhfi»iensis, adult and young with a similar form of whorl. Fig. 10 an unusually turbinate 

 form of PL tenuis. 



Line 1), figs. 1-2 PL Steinheimensis for comparison with figs. 3-4 PL leris, Undorf Fig. 5 PL Steinheim- 

 ensis with sub-angulnr outer whorl for comparison with fig. C PL leris, Undorf. Figs. 7, 8 PL Steinheimensis^ 

 younger stages of same variety as fig. 5. 



Line c, figs. 1-3 PL Steinheimensis with very slight nnsymmeti'ical and cylindricMl wliorls, figs. 4, 5 PL 

 Steinheimensis normal variety (see specimens) with cylindrical whorls, figs. 6, 7, normal variety with nnsym- 

 metrical whorls and a deeper, narrower umbilicus on the lower side than in tlie preceding. Fig. 8 PL Stein 

 heimensis var. aeqiiiumbilicatus ? 



Line d, figs. 1-6 specimens of PL Steinheimensis with stouter whorls transitional to those of line c. Fig. 

 7 PL tenuis, fi-om the rocks of the Upjier Tier of the Cloister Ridge. This has young like the adult of PL 

 Stein he imeiis is. 



Line e, fig. 1 PL Steinheimensis with an extremely turbinate tendency expressed in the last whorl. Figs. 

 2-4 are large fine specimens of the normal unsymmetrical varieties, figs. 5-7, are PL sieu!h"!',!'ami. fo'' comparison 

 with these and others below:, for example compare the umbilicus of fig. 7, with fig. 6, line c. 



Line f, figs. 1-3 PL steiSme,ms, somewhat more advanced stage of transition, figs. 4r-7 PL tenuis. 



Line g, PL tenuis. 



Line h, PL discoideus, figs. 1-4 flatter variety with acute cariuations, figs. 5-7 stouter varieties with gener- 

 ally less acute carinations. 



Line i, PL discoieleics with rotundatus-Uke young, showing transitions to the varieties of PL trochiformis 

 having similar young. 



' See in this connection remarks on page 70. ^ See for discussion of figures on this plate, p. 83. 



2 This shell has a much shallower umbilicus than the one 

 figured on pi. 9, fig. 11, and described on p. 12. 



