BRACHIOPODA. 



239 



and the formation of an umbonal or subrostral vault supported by a median 

 septum. 



The geological range of both Clitambonites and Hemipronites is limited to 

 the Lower Silurian. In American faunas the latter group is still unknown, 

 and the former is represented by only two species, Orthisina Verneuili (von Eich- 

 wald), Billings, from the Trenton limestone and the Anticosti fauna, and 

 Hemipronites Americana, Whitfield, a closely allied species, from the Galena 

 horizon of the Trenton, in Wisconsin. 



PoLYT(ECHiA, sub-gcn. nov. 



Plate vii a, figs. 26-30. 



1886. Hemipronites, Whitfield. Bulletin American Museum of Natural History, vol. i, No. 8, p. 300, 



pi. xxiv, fig's. 1-5. 



This name is proposed for the species Hemipronites apicalis, Whitfield, the 

 essential characters of which have been clearly demonstrated by that author. * 

 Mr. Whitfield recognized the distinctive character of this fossil but hesitated 

 to propose a new generic term, which circumstances now require. 



Fig. 11. PolytoscMa apicalis. 

 Transverse section of pedicle-valve, near tlie apex. 



Fig. 12. rolytacMa apicalis. 

 Transverse section near the cardinal mar^^in. 



Diagnosis. Shell small, subtrihedral in contour. Hinge-line straight, about 

 equaling the diameter of the shell. Pedicle-valve with a high, nearly verti- 

 cal cardinal area marked with oblique striations parallel to the lateral margins. 



* In a provisional list of the genera of jialajozoic brachiopoda, publislied in the Eiglilh Annual Report 

 of the State Geologist (p. 44, 1889), the name Waagenia was used with the intention of applj'ing it to this 

 sub-g-enus, but it appears that both Waagbnia and Waagenblla are preoccupied terms, therefore pi'eclud- 

 mg this intended expression of esteem and appreciation for the invaluable services of Dr. Waagen in this 

 department of science. 



