356 P. E. Raymond — Fauna of the Chazy Limestone. 



all three divisions. This member is further marked by the 

 appearance of the earliest of American Bryozoa, and these, 

 unlike most Ordovician species, range throughout the entire 

 formation above the sandstone. 



Division 1 is characterized by the predominance of individ- 

 uals and species of Braehiopoda. Fourteen of the 25 species 

 of this group occurring in the Chazy of the Champlain Valley 

 are found in this lowest member, while only 2 of the 16 pelec- 

 ypods are represented. Exactly half the species of trilobites 

 are also found here, but specimens are not common. Gastro- 

 pods are more numerous, as half the species are represented 

 and individuals of some forms are abundant. They do not 

 occur in the lower strata, but are confined almost entirely to 

 the upper part. 



There are three zones in this division which are worthy of 

 notice : — 



Zone l a , or the Orthis acutiplicata zone, is near the base of 

 the division and is found at Valcour Island and Isle La Motte. 

 The characteristic fossils are : Orthis acutiplieata, Rafines- 

 quina incrassata, Isotelus harrisi, and Thaleops .ovata, all 

 long rangers except the first. 



Zone l b . The Scalites angulatus zone. The faunule of 

 this zone is found at Plattsburg and Chazy. It is located 

 near the middle of Division 1. The characteristic fossils are : 

 Scalites angulatus, Raphistoma immaturum, R. stamineum, 

 Bucania sulcatina, Camarella longirostris, Illmnus globosus, 

 and Thaleops ovata. Only the first two are restricted to this 

 horizon. 



Zone l c , the Lophospira subabbreviata zone, has been found 

 only at Chazy, but is very strongly marked. It occurs about 

 75 feet below the top of Division 1. The characteristic fossils 

 are : Lophospira subabhreviata and Raphistoma stamineum, 

 both of which are very abundant. Of less importance are the 

 rare Schizambon? duplicimuriatus, Ileliomera sol, and 

 Clionychia marginalis sp. nov. 



Division 2. The Maclurites magna Division. — The strata 

 of this middle division are usually heavy bedded, dark blue and 

 grey, fairly pure limestones, with an occasional layer of grey 

 sparkling dolomite or of light coarse-grained limestone. The 

 layers near the middle usually weather into nodular masses, 

 and the fossils are frequently poorly preserved and difficult to 

 extract. The thickness varies from 200 feet at Chazy to 400 

 at Yalcour Island, and decreases toward the south. The char- 

 acteristic fossils are : Maclurites magna, Rafinesquina cham- 

 plainensis, Plmsiomysplatys, P. strophomenoides sp. nov., Stre- 

 phochetus, Eospongia varians, Eotomaria obsoletum sp. nov., 

 Eccyliopterus fredericus, Bathyurellus minor, Glaphurus 

 primus, and Leperditia limatula sp. nov. 



