6 HYATT ON THE TERTIARY SPECIES 



The adoption of the name Planoibis, was made after due consideration of the different 

 views advanced, but especially after a close study of the affinities pointed out by Prof. 

 Sandberger, in his renowned work on the " Land-und Siiswasser-Conchylien der Vorwelt." 

 The name of Valvata does not seem to apply, for two reasons ; the entire absence of the 

 least remnant of an operculum, although I searched for this part with a microscope in 

 the loose sands as well as in the limestones ; and the peculiar asj^ect of the striae of growth 

 which are curved, even in the unwound forms, instead of being annular, as in the Valvata 

 forms. 



The affinity with Carinifex, which Prof. Sandberger insists upon for most of the series, 

 does not appear to me so close as that with many species of Planorbis. His authority 

 with regard to a matter of this sort would naturally and rightfully have more weight than 

 mine, but he describes PI. Steinheimensis, and some other forms, which I am entirely 

 unable to separate from the carinated varieties or S23ecies, as members of the genus 

 Planorbis, whereas the remainder appear under the generic name of Carinifex. The 

 young of Carinifex Camphelli, the only form I have been able to obtain, either from 

 the Smithsonian Institution, the Museum of Comparative Zoology, or any of my 

 correspondents, is entirely distinct in form from most of the young forms of PI. discoideus 

 and PI. trochiformis, though to others it bears a very close resemblance. I am not at all 

 surprised that Piof. Sandberger should join the two in view of this similarity, but 

 on account of the evident connection of PL trochiformis with PI. levis, I cannot support 

 him in this conclusion. In my opinion, it must be regarded as a similarity produced 

 in the shell of distinct animals in widely separated localities. 



The nomenclature adopted for the various forms, is similar to that of Dr. Hilgendorf 's, 



in so far as the main forms are represented by distinct names, generally the same as those 



proposed by him, with the omission of the name " multiformis," and the intermediate forms 



are designated by two names placed one above the other, thus steinheTmlusis- I" this way 



the derivation of these forms and their intermediate character is conveniently expressed in 



one and the same term. I have used the binomial nomenclature instead of the trinomial, 



because the latter is clumsy ; and I can see no reason for the prevalent practice 



of designating under the same specific name all forms which may be joined by intermediate 



forms or by the study of their development. It is evident, that all of the principal forms 



of the PI. trochiformis series differ from each other quite as much as the universally 



recognized and distinct species of the main body of the genus. If they had been found 



in different localities, there would be no hesitation in describing them as species. A 



binomial nomenclature, therefore expresses exactly the sense which it is considered 



desirable to convey, namely, that the forms dealt with in this memoir are, as compared 



with others of their own group, of sj^ecific value, and ought, from a taxonomic point 



of view, to be so considered. 



In conclusion, it seems essential to add, that, in spite of the great care taken at the 

 time the explorations were made to render the evidence as perfect as possible, many 

 things were necessarily neglected. Thus a fuller exploration of the Valley Rocks, 

 especially with regard to the relations of the Cloister Ridge Rocks, and the Pit Deposits 

 can only be attained by these or similar means. Doubtless Dr. Hilgendorf 's forthcoming 

 memoir will supply many of these deficiencies. Nevertheless, the existence of a Lower 



