Geol.— Vol. I.] SMITH— COMPARATIVE STRATIGRAPHY, 393 



in the Himalayas, and in California, where it is represented 

 by Tropttes subbullatus Hauer, T. lorquillus Mojsisovics, 

 T. dilleri Smith, sp. nov., and many other species. 



Tropites dilleri Smith, sp. nov. 



Plate XLVI, Figs. 3-4; Plate XLVII, Fig. 3. 



Involute, robust, whorls broad and helmet-shaped, curving gently from the 

 subangular umbilical shoulder to the venter, without any abdominal shoulders. 

 The umbilicus is rather narrow, with steep inner walls, exposing the umbilical 

 shoulders of the inner whorls. There are weak umbilical knots, and from 

 these faint ribs run forward with a gentle curve over the flanks. There are 

 also distinct fine spiral lines covering the entire shell. The ribs show on the 

 cast as well as the outer shell, while the spiral lines are visible only on the 

 outer shell. In the middle of the venter there is a low keel, bordered by 

 deep keel furrows, which show much more distinctly on the cast than on the 

 outer shell. 



The height of the whorl is less than one-half the diameter of the shell, the 

 width is one and three-fifths times the height, and the whorl is indented to 

 more than one-third of the height by the inner volution. The umbilicus is 

 about one-sixth of the total diameter of the shell, becoming wider and showing 

 egression with age. Also the whorl becomes higher and narrower in propor- 

 tion, as maturity advances. 



The septa are ammonitic, dolichophyllic, exactly like those of Tropites 

 subbullatus, to which T. dilleri is nearly related. 



It differs from T. suhhiillatus only in the narrower, higher 

 whorl, but this difference is constant even in the early ado- 

 lescent stages. T. dilleri is intermediate between T. siib- 

 bullatus and T. torqiiillus ; it differs from the latter species 

 in the broader, lower whorl, and in the slightly wider umbil- 

 icus. It may be identical with the form described by 

 Mojsisovics' as a variety of Tropites torqiiilliis, which 

 differs from the species to which it is ascribed, in the 

 broader whorl, and wider umbilicus. T. dilleri differs 

 from T. discobiillatus in these same characters, only to a 

 greater degree, for that species is more compressed even 

 than T. torqiiillus. It seems to the writer that Mojsisovics 

 has drawn the lines too sharply in the discrimination of the 

 Hallstatt species, and that there is no possibility of follow- 

 ing this discrimination in working over similar material. 



1 See Bibliog. 23— II, pi. cvi, fig. 4. 



