ACADEMY OF NATURAL SCIENCES. 383 



between mormonum and ramentosa, and we also find specimens connecting the 

 latter with 25, 26, and perhaps others. 



Occasional links also occur, connecting many others of the banded species to- 

 gether. 



A similar intermixing of species, where nearly allied, occurs among our ma- 

 rine shells wherever two or more encroach on each other's limits ; but the com- 

 parative rarity of the intermediate forms seems to indicate hybridity rather than 

 specific identity of their allies. 



It is probable that groups X and XI and XIII and XIV should be united, as the 

 distinctive characters between them are not of first importance, and species of each 

 are very closely similar otherwise. Parallel columns may be formed, as indicated 

 on p. 260, in which close resemblances in form, number of whorls, etc., between 

 species of the different groups may be shown, and this may be extended so as 

 to show analogous parallels with those of other subfamilies, or even families, 

 but these resemblances do not indicate affinity, though very likely to mislead. 

 A geographical arrangement of some groups is also indicated, though imper- 

 fectly, as there are no impassable limits between them. For special localities of 

 many species, see vol. Ill, pp. 62, 115, 180, 259, and II, 91, 103.* 



The Darwinian theory of development might be very beautifully illustrated by 

 these banded snails, if we could find evidence that their various forms had all origi- 

 nated from a common stock (which might be the ramentosa, as that species now 

 occupies a nearly central locality). But though fossil forms have been found 

 differing considerably from their present representatives, there are others appa- 

 rently as old, which show no such differences, and none of them show a tendency 

 towards any common original type. The one referred to by Professor Whit- 

 ney on p. 278, as found with the human skull of supposed pliocene (?) age, does 

 not differ perceptibly from specimens of mormonum, now living near the local- 

 ity. It retains even its band of color, which is soon lost in specimens imbedded 

 near the surface, and this (if not preserved by its deep burial or incrustation) 

 is strong evidence against a great antiquity of the skull. All other fossil Heli- 

 coids are considered postpliocene, at least so far as known in this State, though 

 extinct species occur in Europe as far back as the Eocene. 



The bandless species of the west coast slope, from lat. 33° to 49°, are added 

 to the synopsis, to show their relations and analogies with the banded. The 

 arrangement followed is essentially that of Tryon, except the addition of some 

 he has omitted, or not yet published. The generic divisions are also reduced to 

 groups, as the true generic characters are not yet settled. The lip is entirely 

 wanting in the -first family, but in the bandless Helicida of this coast, it becomes 

 of great importance for grouping of species, (49 to 55) of which we have very 

 few, while east of the Rocky Mountains there are more than fifly. Group III 

 is also largely developed on the Atlantic slopes. The tendency now is 

 to divide too much, which is as unnatural as to unite all under genus Helix, 

 as many still do. It is probable that the divisions here called subfamilies, an- 

 swer more nearly to the true genera than any others, though they require modi- 



See, also, the " Gcognphical Catalogue of West Coast Mollasca,'' published by the State Geo- 

 logical Survey, April, 1867. 



