Report of the State Geologist. 431 



genus is well developed in the Silurian and may be considered as a 

 forerunner of the more abundant naticoids of the Devonian and 

 Carboniferous. 



Brachiopods. The Orthids attain an important development both 

 individually and specifically. The abundance of Orthis is itself sug- 

 gestive of Silurian faunas; moreover, the types of 0. elegantula and 

 0. hybrida are represented, the former by 0. planoconvexa, 0. subcari- 

 nata, the latter by 0. discus, etc. These types are continued into the 

 Devonian with a feebler representation, e. g. 0. lenticulams, Upper 

 Helderberg, 0. lepida, Hamilton. 



The abundant 0. oblata marks the inception of a characteristic 

 Devonian group, that of 0. Vanuxemi, in which valves are large, 

 subcircular, subequiconvex, the muscular impressions flabellate (0. 

 musculosa, Oriskany, 0. peloris, Schoharie grit, 0. Lima, Corniferous, 

 0. Vanuxemi, Penelope, leucosia, idoneus, Hamilton, 0. subcordiformis 

 Eifelian). 



Orthis varica (Dicoelosia) is a Silurian type. Scenidium (insigne) is a 

 rare form occurring in about equal development in both Niagara and 

 Middle-Devonian faunas (Mystrophora, Eifel). 



The Strophomenoids (Strophomena rhomboidalis, Strophodonta, Stro- 

 phonella) are very abundant and much diversified. Their develop- 

 ment is in harmony with their great representation in the Upper 

 Helderberg and Hamilton. It is possible to trace various features in 

 this group which attain characteristic development in either Silurian 

 or Devonian faunas; e. g. the abundance of reversed Strophomenas 

 (Strophonella), (Silurian); of true Strophodonta (Devonian); flat species 

 of the group of Strophodonta perplana (Devonian); convex forms with 

 full, rounded umbones (Devonian); convex forms with flat umbonal 

 regions and anterior deflection (Silurian). S. varistriata has a peculiar 

 undulated ornamentation between the radiating lines, a feature 

 reproduced in the S. Paiersoni of the Upper Helderberg. Strep- 

 torhynchus of typical character, with high, often distorted ventral 

 beak, makes its first appearance in the species S. deforme. 



Ghonetes is represented by two undescribed species,* one a large 

 flat form very closely similar to the Oriskany species, G. complanata, 

 belonging to the group of G. syrtalis (Devonian) ; the other a small, 

 convex species, belonging to the extensive Devonian group including 

 G. lineata, scitula, lepida, deflecta, etc., etc. 



The Spirifers constitute a striking feature of the fauna, their 

 abundance and variety being in great contrast to their comparative 

 paucity in the Niagara. In S. perlamellosa we have the first of the 



* In the collection of Mr. Schuchert. 



