Raymond : Brachiopoda and Ostracoda of the Chazy. 239 



Orlhis plalys Billings, 1863. Geology of Canada, p. 129, fig. 54. 



Orlhis plalys Hall and CLAuicn:, 1892. Paleontology of Now York, Vol. VIII, 



pt. I, p. 2l8. 

 Orlhis plalys Winchell and Schuchert, 1893, Paleontology Minnesota. V'ol. Ill, 



pt. I, p. 424. 

 Dinorthis plalys Schuchert, 1897. Bulk-tin United States Geological Survey, 



No. 87. 



In the first part of Volume VIII of the "Pa!eontoU)gy of New York," 

 Hall and Clarke proposed to divide the reversed impunctate Orthids 

 into three groups: first, that of Orthis pectinella, for which the name 

 Dinorthis was proposed, second, the group of Orthis subquadrata, with 

 the name Plccsiomys, and third, the group of Orthis sinuata, called 

 by them Ilcbertella. Winchell and Schuchert, in the Paleontology 

 of Minnesota, rejected the name Plcesiomys, and show that there were 

 species and varieties with all gradations in the striae from the very 

 finely striated forms like Orthis deflecta to the coarsely plicated shells 

 like 0. pectinella. While this is doubtless true, it seems best to retain 

 the name Plcesiomys for the present, and apply it to such forms as 

 Orthis subquadrata and 0. platys, in which the surface is not coarsely 

 plicated, but is covered with striations which increase by bifurcation 

 and implantation. 



Description. 



Pedicle valve fairly high and convex on the umbo, flat or only 

 slightly convex in front. Brachial valve nearly flat, usually showing 

 a shallow sinus on the umbo. Surface marked by fairly coarse striae, 

 which increase by implantation. There are usually three or four in 

 the space of two millimeters on the front of the shell. The interior 

 of the pedicle valve shows a small muscle area under the beak, composed 

 of two strong diductor scars, and between them two very narrow ad- 

 ductor scars. Delthyrium narrow. No specimen has been seen 

 which was so preserved as to retain the deltidium. In the brachial 

 valve there is a low median septum. Other details could not be made 

 out. 



Locality. — This species is rather common at Crown Point, and less 

 common at Valcour Island, Chazy, and Montreal. It usually occurs 

 in a partially exfoliated condition. 



Subgenus \\\lcourea nov. 

 This subgenus is proposed for impunctate orthids with reversed 

 valves, strophomcnoid habit, well developed deltidium, simple cardinal 



