STRATIGRAPHY. 
39 
The list of species is as follows: 
Ostrea inornata M. and H. 
Ostrea plumosa Morton. 
Syncylonema rigida (H. and M.). 
Avicula linguaeformis E. and S. 
Inoceramus cripsii var. barabini Morton. 
Inoceramus sagensis Owen. 
Inoceramus sagensis Owen, var. 
Inoceramus n. sp. 
Modiola meeki (E. and S.). 
Pinna lakesi White. 
Limopsis parvula M. and H. 
Eriphyla gregaria M. and H. 
Liopistha (Cymella) undata M. and H. 
Dentalium gracile H. and M. 
Margarita nebrascensis M. and H. 
Lunatia occidentalis M. and H. 
Anchura rostrata (Gabb). 
Cerithiopsis moreauensis M. and H. 
Fasciolaria (Piestochilus) alleni White. 
Fusus (Serrifusus) dakotensis M. and H. 
var. 
Baculites ovatus Say. 
Placenticeras placenta (Dekay). 
Placenticeras placenta var. intcrcalare 
M. and H. 
Ptychoceras mortoni M. and H. (?). 
Ptychoceras crassum Whitfield. 
Heteroceras angulatum M. and II. (?). 
Heteroceras nebrascense M. and II. 
Heteroceras cochleatum M. and H. 
Emperoceras beecheri Hyatt (?). 
Helicoceras mortoni var. tenuicostatum 
M. and H. 
Scaphites nodosus var. brevis Meek. 
The other fossiliferous horizon, which is 300 or 400 feet lower, yields many of the 
naine species, together with a few others that seem to be peculiar to it, as will be seen 
by the following list: 
Ostrea pellucida M. and H. 
Ostrea inornata M. and H. 
Anomia sp. 
Syncyclonema rigida (H. and M.). 
Camptonectes cf. parvus Whitfield. 
Avicula linguseformis E. and S. 
Avicula nebrascana E. and S. 
Gervillia sp. 
Inoceramus cripsii var. barabini Morton. 
Inoceramus sagensis var. nebrascensis 
Owen. 
Inoceramus pertenuis M. and H. 
Modiola alternata M. and H. 
Pinna lakesi White. 
Yoldia evansana M. and H. 
Trigonia n. sp. 
Caprinella coralloidea H. and M. 
Protocardia subquadrata (E. and S.). 
Cardium speciosum M. and H. 
Legumen planulatum Conrad. 
Tellina scitula M. and H. 
Glycimeris berthoudi White. 
Anatina sp. 
Liopistha (Cymella) undata M. and H. 
Mactra sp. 
Dentalium gracile H. and M. 
Lunatia occidentals M. and H. 
Vanikoro ambigua M. and H. 
Margarita nebrascensis M. and H. 
Anchura americana (E. and S.). 
Anchura rostrata (Gabb). 
Aporrhais meeki Whitf. (?). 
Fusus (Serrifusus) dakotensis M. and H. 
Pyrifusus newberryi M. and H. (?). 
Fasciolaria (Mesorhytis) gracilenta M. and 
H. (?). 
Anisomyon borealis M. and H. 
Anisomyon patelliformis M. and H. 
Cylichna sp. 
Actseon sp. 
Pachydiscus complexus (H. and M.). 
Placenticeras placenta var. intercalare 
M. and H. 
Baculites ovatus Say. 
Ptychoceras crassum Whitf. 
Heteroceras sp. 
Helicoceras mortoni var. tenuicostatum 
M. and II. 
The species of these lists arc nearly all of common occurrence in the Montana forma- 
tion of the Rocky Mountain region, but a few of them are worthy of special aotice. 
Pachydiscus complexus (II. and M.). which has hitherto been known from a tew im- 
mature specimens, is here not rare, and attains a diameter of 6 or 8 inches. At leasl 
two other species not hitherto reported from I he Xorthwest — Legumen planulatum and 
Anchura rostrata — are common in the Ripley beds of Alabama, Mississippi, and Texas, 
and the undescribed Trigonia is closely related to T. eufalensis, also from the Kipley. 
