70 HYATT ON THE TERTIARY SPECIES 



carinae are distinctly indicated in fig. 1, line c, and the first, second, third, and fourth in 

 some other specimens of the turretted varieties, there are no accompanying indications 

 of sulcations on the upper sides of the whorls. These are usually round, but may become 

 somewhat flattened, though in no case have I found sulcations. The limits here given 

 for this species correspond quite closely to those given by Sandberger, since 

 he also included under one name the three principal varieties described by Hilgendorf. 

 The difference in our views is due to the intermediate forms, which in my opinion bridge 

 the chasm between this and PI. levis. With regard to the affinity with Carinifex, I have 

 written elsewhere. 



The whole series is given on pi. 6. 



Figs. 1-3, line a, are PI. levis, from Undorf. Compare fig. 1, line a, with fig. 1, line b ; 

 also fig. 2 with 4, line a, and fig. 3 with 7, line a. Line h is the PI. "^^fe^"™"', from formations 

 I and m, of the Cloister Pits. Thus it can be seen, that it is not necessary even to descend 

 to formation a of the pits, in order to obtain forms showing the probably direct derivation 

 of PL oxystomus from PI. levis. 



Fig. 3, line b, is important in this connection, because it shows very distinctly that a 

 perfectly preserved shell of PI. "■^^eS"* exhibits the bright and polished surface and 

 striae which are common in PL levis. 



The transition from PL levis to PL oxystomus is also still farther confirmed by the two 

 young specimens, figs. 4-5, line d ; fig. 5, being PL levis, from Undorf, and fig. 4, the 

 young of a typical PL oxystomus, from the Cloister Pit. 



PL oxystomus var. "^^4^°™"* is shown in figs. 4-7, line a ; these are even closer to PL levis 

 than those on line b, which exhibit the transitions from "^"ievu^^ to true oxystomus, 

 occupying lines c and d. 



PL supremus is represented by the figures on line e. 



The series is roughly shown by the range of figures numbered 1 in each line, and these 

 exhibit the general tendency to increase the spirality. The tendency in each variety to 

 increase spirality of growth in some shells, is also observable. Thus, in PL oxystomus, line c, 

 fig. 6 is quite trochiform, only inferior to fig. 1, line d, a specimen of the same variety. 



This last is apparently quite as turbinate as fig. 1, line e, a specimen of PL supremus ; 

 but in reality it is not of the same species as this, since the umbilicus is more open, and 

 wider. 



The oxystomus-like widening of the whorl in course of growth, fig. 1, line c, is not 

 observable in any of the forms of PL levis, in the youngest stages of growth, which have 

 whorls like fig. 3, line a. In PL "^^1^°™", this peculiar widening, occasioning the angularity 

 of the aperture on the lower side, is more pronounced in the adults, and appears earlier 

 in the life of the individual. In PL oxystomus, line c, fig. 5, this is still more pro- 

 nounced, and inherited at a still earlier stage. 



In PL supremus the broad whorl occurs at a very early age, so that the youno- are 

 often identical with the typical form of oxystom.us ; and subsequently the first carination, 

 or the first and second with the sulcation between them, appears during the growth of 

 individuals. 



It is interesting, also, to note that some specimens which have no pronounced carin- 

 ations or sulcation, but are smooth, like oxystomus, have to be classed with this variety on 

 account of the peculiar shape of the whorls, as in the turbinate form, fig. 1, line e. 



