94 HYATT ON THE TERTIARY SPECIES 



approximate very closely to trocMformis. PI. sulcatus had the same peculiarities in the 

 • middle bed. In the upper bed, however, nearly all the forms, without approximating 

 very closely to PI. trocMformis, showed the trochiform tendency in being more or less 

 spiral, either throughout life, or only in the adult ; only a very few of the flat sulcatus 

 form were found in this part. PI. minutus occurred but very rarely in the lower part, 

 while in the middle part it was much more numerous, and also associated with PI. costatus. 

 In the upper part they were even more numerous, and associated with PI. costatus. One 

 specimen had the tunnelled form, but the whorls were not open. Var. Kraiissii follows 

 nearly the same rule, being scarce in the first, quite numerous in the second, and still more 

 abundant in the third part. 



One broken specimen of PI. oxystomus was found in the middle part in which only a 

 portion of the centre, and an outer whorl is left unbroken. 



Formation " g," East Pit. 



This consists of clay, but has two pockets or layers of shells. PI. discoideiis was very 

 abundant, with numerous specimens of the rotundatus young of PI. trocMformis in all 

 varieties, PL minutus and costatus, and PI. parvus, and rarely PI. crescens. 



Formation " h.," East Pit. 



This consists of shell-sand. PI. discoideus, and PI. trocMformis, with all the interme- 

 diate forms were very abundant. PI. m,inutus and PI. costatus were also very abundant, 

 and uncoiled forms of both species. Var. Kraussii and PI. crescens also occur, but not so 

 frequently. 



Formation " i," East Pit. 



This consists in the lower part of two strata of clay, with three of shell-sand, and in 

 the upper part of one layer of shell-sand between two of limestone. The shells were 

 not abundant, and much thinner than in the preceding formations. PI. trocMformis most 

 frequently occurred, but not in good preservation. PI. minutus, PI. costatus, and 

 PI. crescens were also found. A specimen similar to PI. pseudotenuis Hilg., probably the 

 young of PI. tenuis, occurs for the first time in these formations. 



Formation "k, 1," East Pit. 



This consisted of shell-sand and could have been divided into two parts according to the 

 fauna, but this hardly seemed essential since the deposit was continuous. The lower part 

 contained PI. mhiutus, PI. costatus, and a large proportion of the uncoiled or costated 

 denudatus-like varieties. PI. crescens, and PI. oxystomus also occurred, the latter in 

 great plenty. PI. trocMformis was also abundant, but the most interesting form 

 zoologically, though not frequent, was the pseudotenuis-like species, which seems to be the 

 young of the PL tenuis figured on line/, figs. 1-6, plate 2. 



The shells of PL mi?iutus, in the upper part, were whiter and more fragile than in the 

 lower, and PL oxystomus was almost entirely absent ; otherwise the fauna presented the 

 same characteristics. 



