32 HYATT ON THE TERTIARY SPECIES 



mens of Planorbis from this vicinity, or from the West^ there is no difficulty in deter- 

 mining that they are the result of the unusual and unfavorable conditions to which the 

 individuals or races were exposed. They all show one thing, namely, a disturbance of 

 the regular growth of the spiral, resulting in some extreme cases in the complete unroll- 

 ing of the whorls. 



This enables us to separate them at once from such series as are presented in the 

 third sub-series, and Second, Third, and Fourth Series on pi. 9, and adds considerably to 

 the evidence here produced. This question undeservedly assumed great prominence in 

 the discussion of the Steinheim shells, at the meeting of the Naturforschende Gesellschaft 

 at Munich, several naturalists hastily adopting the view that most of these shells were 

 distorted forms. 



I must also be permitted to point out another serious error which the retrogressive 

 sub-series illustrate. Many investigators evidently picture a retrogressive series as a 

 departure from the normal form of any group, which can only be represented by 

 a line running backwards, so that to them the fan-shaped ari-angement of lines is not a 

 true presentation of the affinities of any given number of series. They demand a series 

 of radii emanating from a centre to all points of the periphery of a sphere. The utmost 

 that can be granted to the graphic presentation of such an arrangement is a hemisphere 

 of radiating lines. A centre of distribution being granted, that centre is a form or 

 fixed point in geologic time, and from that we can only truthfully depart in lines 

 of genetic descent, radiating in time upwards, or horizontally, perhaps, but never 

 backwards. 



This common sense view of the relations of affinity and time is farther borne out 

 by the fact, that in no case are retrogressive series actual returns of forms really 

 identicalwith those previously existing, unless they are the direct descendants of those 

 forms. The Baculite is not an Orthoceras, nor is Bactrites, though they are all 

 wonderfully similar. The Epizoa are never Protozoa, nor is Entoconcha a worm. Nor 

 are the distorted forms of Magnon,^ though Planorbes, identical with their distorted 

 brethren of the Steinheim basin, though this is a case where identity could perhaps be 

 found, if the environment was exactly similar, and they belonged to the same species. If 

 the retrogressive sub-series can be represented by lines going backwards, where are the 

 more ancient forms with which they are identical ? 



It cannot be claimed that the Magnon specimens should be graphically represented in 

 this way, because they are sunilar to those of Steinheim ; for it is evident that they are 

 simply parallel forms. As compared with the normal Planorbis, they can be more 

 truthfully represented by the extreme lateral line of a fan-shaped arrangement of lines 

 having a centre, in some existmg species of Planorbis. 



The habit of representing affinities by the sphere of radiating lines is in direct 

 opposition to all that we know about genesis, growth, and development, retrogressive or 

 progressive, and the relations of these phenomena to time and the surfaces upon which 

 animals live. I may add, also, that it is rarely employed by any, but mere zoologists. 



' U. S. Geol. anil Geo"-. Survey of Colorado, Dr. F. V. ^ M. Louis Pire. Planorbis complanatus (forme scalaire). 



Hayden, 1874. Report by Ernest Ingersoll, p. 402. Ann. Soc. Malacol. Brussels, vol. 6, 1871. 



