THE FAUNAS AND THEIK RELATIONSHIPS 415 



Strophomena filitexta, Parastrophia schqfieldii Winchell and Schuchert, 

 Triplecia sp. nov.. having the general appearance of Platystrophia ; Heher- 

 tella bellirugosa (Conrad), Platystrophia biforata (Schlotheim), Streptelasma 

 cornicidum Hall, Receptaculites occidentalis Salter, Prasopora simulatrix 

 orientalis Ulrich, Hemiphragma ottaivaense Foord, Rhinidictya mutabilis 

 Ulrich. Hemiphragma is exceedingly abundant in the upper part of 

 this horizon and is its most characteristic fossil. 



Horizon A-8 may be regarded as the basal zone of the Trenton. It is 

 marked by the abundant remains of a homalonotoid trilobite, Brong- 

 niartia irentonensis (Simpson). Other fossils occurring in this zone are 

 Trinudeus concentricus, Isotelus platycephalus, Cytoceras camurum Hall, 

 Protowarthia tenuissima sp. nov., Rafinesquina alternata (Emmons), Dal- 

 manella testudinaria (Dalman), Orthis tricenaria Conrad. 



In horizon A-9 trilobites are especially abundant. They include 

 Isotelus platycephalus, Pterygometopus callicephalus, Rlsenus crassicauda, and 

 Encrinus tuberculosus sp. nov. Other fossils are Tetranata obsoleta, Orthis 

 tricenaria, Plectambonites sericeus (Sowerby), Rafinesquina alternata, Para- 

 strophia scofieldii, Dinorthis subquadrata (Hall), Plectorthis plicatella (Hall), 

 Cornidites flexuosus Hall, Hemiphragma ottawaense. 



Few varieties of fossils are found in horizon A-10. Plectambonites 

 sericeus occurs in abundance, and also Rafinesquina alternata. Lingida 

 riciniformis Hall also occurs. 



The rocks in horizon A-11 are shales chiefly and nearly unfossiliferous. 

 Plectambonites sericeus is the only form noticed. 



In horizon A-12 an abundance of gasteropods is the most notable 

 feature. The principal forms represented are Tetranota bidorsata (Hall), 

 Hormotoma bellicincta (Hall), Liospira americana (Billings), Murchis'onia 

 tricarinata Hall, Lophospira bicincta (Hall), Subulites canadensis Ulrich, 

 Gonradella grandis Ulrich, Eccyliomphalus undulatus (Hall), Salpingostoma 

 canadensis (Billings), Salpingostoma buelli (Whitfield), Fusispira angusta 

 Ulrich. Other fossils found are Ceraurus pleurexanthemus, Isotelus platy- 

 cephalus, Illsenus crassicauda, Orthoceras strigatum Hall, 0. textile Hall, 

 Triptoceras hastatum (Billings), Orthis tricenaria, Dinorthis pectinella (Em- 

 mons), Plectorthis plicatella, Rafinesquina alternata, Plectambonites sericeus, 

 Hemiphragma ottawaense. 



Horizon A-13 resembles A-11 in all respects. It is a thin bed of 

 shale, in which Plectambonites sericeus occurs abundantly, especially in 

 the limestone lenses, which are found in the shale. 



In horizon A-14 Plectambonites sericeus and Rafinesquina alternata occur 

 in great numbers. Plectorthis plicatella and Dalmanella testudinaria are 

 found occasionally. 



Horizon A-15 is especially marked by the abundance of Salpingostomy 



LVIII— Bum,. Gf.oi,. Soc. Am.. Vot,. U, 1902 



