344 



N\-. STANTON INVERTEBRATE FAUNA OF THE MORRISON 



Limnwa ativuncula White 

 Limnwa consortis White 

 Limnwa ? acccleratu Wliite 

 Planorhis vcternns M. and H. 



Darwinula Icguminella Forbes 

 Gypris purheckensis (Forbes) 

 Cypris sp. 



Of these, se\en species are referred to Vnio, three to Liinnaa, one each 

 It) Planorhis, VorHcifex, Valvata, Yivipanis, Lioplacoiles, and Neritina, 

 and five are ostracod crustaceans. All are of fresh-water habitat. More 

 than half of them come from a single locality near Canon City, Colorado. 

 Tlie others are I'cported from the Black Hills, from two localities in 

 southern Wyoming, and from the head of Wind Eiver, Wyoming, the 

 stratigraphic position of the species from the la-st-named locality being 

 doubtful. Logan^ has listed five species from the Freeze-ont Hills, south- 

 ern AVyoming, of which three species of Unio and a ^'a■h^ala are described 

 as new. The list is as follows: 



Unio bailcyi Logan 

 Unio knighti T^ogan 

 Unio wiUistoni Logan 



All from Fi'eeze-out Hills. 



ValiHita led Logan 

 Planoybis vctcrnus M. and H. 



T'^ndescribed collections fi'oni Morrisf»n, Colorado City, and Uncom- 

 paligre Valley, Colorado, from the Black Hills, from the neighborhood 

 of Como, Wyoming, aiul of Jensen, Utah, and J'loiu tlic Creat Falls and 

 Lewistown areas in Montana, have added to tlie Morrison fauna without 

 changing its essential characteristics until, as now known, it includes 

 about 30 species, practically all of which are referred to living genera. 



Comparison w riii otieer non-Makixk ixvertebeate Faunas 



WEALD EN FAUNA 



From the statement tliat tlie fauna consists of fresh-water MoUusca 

 and Ostracoda belonging to modern genera, it is t'\ ident that it can offer 

 little direct evidence on the exact age of the Moi risoii foi-iiiation. Logan's 

 argument foi- convlatiiig tlie Morrison with the WCaldcii because, as he 

 says, "four of the genera — I'nio. \'iilv(tln. Flanuihis. and Viviparus — 

 which are represented in the two formations by species having practically 

 the same degree of de\('lo]»iiient are not known fi'oni older formations," 

 is not valid because it does not agree with tlie facts of distribution as now 

 known, rnio. Planorhis. and Valvata are all known fioni formations 

 older than the AYealden. and the species of Unio from the Upjier Triassic 



3 W. N. Logan : The stratigraphj- and invertebrate faunas of the Jurassic formation 

 in the Freeze-out Hills of Wyoming. Kansas Univ. Quarterly, vol. 9, 1900, pp. 132-1.34.' 



