220 THE DEVONIAN OF MISSOURI. 



The characteristic Atrypa reticularis is but meagerly repre- 

 sented, and only in the upper beds. The cosmopolitan Anoplo- 

 theca flabellites is rarely present, and so far as known is restricted 

 to the lower beds. Spirifer arenosus and Spirifer murchisoni are 

 present in greater abundance. The Meristellid brachipods show 

 distinct differences from described forms, and are represented 

 by at least four new species, which are restricted to the lower 

 beds. 



The following species of brachiopods range through both 

 horizons: Rhipidomella emarginata, Dalmanella oriskania, Rhipi- 

 domella musculosa, Leptaeria ventricosa, Leptostrophia magnified, 

 Leptostrophia magniventra, Chonostrophia complanata, Eatonia 

 peculiaris, Plethorhyncha principalis, Rensselaeria ovoides, Rens- 

 selaeria cf. steward, Spirifer arenosus and Spirifer murchisoni. 



A few fragments of Pelecypods occur in the lower beds 

 but these present no diagnostic characters. 



Quantitatively the gastropods come next in importance to 

 the brachiopods. The assemblage is particularly characterized 

 by the Platycerid type, and they present the characteristic lower 

 Devonian aspect. They are for the most part restricted to the 

 lower beds, 18 species occurring there, while only 6 occur in the 

 upper. Only 3 species persist through both horizons. These are: 

 Platyceras nodosum, Platyceras planovolvis and Diaphorostoma 

 ventricosa. Of the 21 species which have been identified, five 

 species and one variety are new, or approximately 28 per cent 

 of the whole. Of the remainder, 10 occur in the Oriskany else- 

 where, and 7 in the Helderbergian. One form, Platyceras 

 dumosum, is an Onondagan species. Four of the species range 

 through the Helderberg and the Oriskany. These are: Platyceras 

 gebhardi, Platyceras newberri, Platyceras reflexum and Diaphoros- 

 toma ventricosum. One form, Platyceras peregrinus, belongs to 

 that type of laterally compressed Platycerid shells, which is so 

 common among the South American faunas. 



The trilobites, although not represented by numerous indi- 

 viduals, belong to 17 different species. The specimens are all 

 fragmentary, and not one entire example has been observed. 

 Twelve species occur in the lower beds, and 7 in the upper, only 

 2 of these, Proetus protuberans and Phacops cristata, ranging 

 through both horizons. Two new species have been described. 

 Of the remainder, four occur in the Oriskany of New York and 

 Maryland, seven in the Helderbergian of New York and Mary- 

 land, and two in the Onondagan of New York. 



