McGee and Call— Loss of Bes Moines, Iowa. 219 



forty-two. These forms are distributed among twenty-five 

 subgenera comprised in eight families. Of the families not 

 included in table I, the A ncylince, Viviparidce and Vah 

 exclusively fresh-water in distribution, while the Rissoidtx com- 

 prise both fresh- water and marine genera. Those enumerated 

 are fresh-water only. The facies of molluscan life seems there- 

 fore to have become decidedly more aquatic in recent times.* 



Some of the forms indicated in table I are widely distributed 

 both in time and space, while several of the subgenera attain a 

 very high antiquity, f Of the families the oldest terrestrial 

 group is the Helicidix% represented by Strophites grandcevus 

 Dawson, from the Erian plant-beds of 'St. John, New Bruns- 

 wick. The subgenus Gonulus dates back to the Carboniferous, 

 being represented by Conidus jirucus Carp., from the South 

 Joggins, Nova Scotia. Of equal age is the subgenus Pupa, 

 represented by four species described in the paper last above 

 cited. Vallonia pulchella and Strobila labyrinthica have each a 

 great antiquity, the last named having, howevei-, the widest 

 distribution. The former is circumpolar, is a hardy species, 

 and is known to abound at comparatively great . 

 Binney quotes Prestwich (Quart. Jour. Geol. Soc, xxvii. p. 

 493) as authority for this species in the Eed and Norwich 

 Crag. || Its wide distribution is suggestive of its great antiquity. 

 The second of these species, Strobila labyrinlhica, is a represen- 

 tative of a now almost exclusively American subgenus, one of 

 whose species, however, occurs in Jamaica. It is distributed 

 over all the Eastern provinces of Binney. From the Eocene of 

 Knglan-.l is recorded an extinct Belix referable to this species. 

 According to Bland the fossil //<;//./■ luhyrinthka from France 

 u is apparently identical with our species.'' Binnev" Rioting 

 Whiteaves (Can. Nat., vol. viii, p. ;.ii,i re<-«.r-ls //. i„h lf rinth:.-a 

 from the Upper Eocene at Headon Hill, Isle of Wight, and in 

 the Paris Basin. Heli ulia may be properly 



considered the •■haraeteri.-.tic f«>s>il "f ail l<>s--deposits in the 

 valley of the Mississippi. 



In similar deposits to that now under consideration in Bel- 

 gium many of the same genera and some few of the same 

 species are found. This is really an important fact as establish- 

 ing the former wide geographical distribution of forms now 

 confined almost solely to one or the other of the two continents. 



f Vide this Journal 



