BRACHIOPODA. 



239 



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

 septum. 



The geological range of both Clitambonites and Hkmu'ronites 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 Eicli- 

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

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

 horizon of the Trenton, in Wisconsin. 



PoLYT(ECHiA, sub-gen. nov. 



Plate vii a, figs. 26-30. 



1886. HfiiiipfDiiiUs. Whitfii-:i.i>. liulletiii Ainei'icau Miiseiiin of N.-itiiral History, vol. i. No. S. ji. HOO. 



pi. xxiv. tijr-'^. !-.'). 



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. Polytachia apicalis. 

 Transverse section of ptMiicIevalvc, m-ar tlur apt'X. 



Frn. 12. rolytachia apicalin 

 Trausvei'se section near tlie canltnal mar^rin. 



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

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

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



* 111 a provisional list of tlie genera of jiahiiozoic biacliiopoiia, pulilishetl in the Eighth Annual Report 

 of the State Geologist (p. 44, 1889), the name Waaoenia was used with the intention of applying it to this 

 sub-genus, but it appears that both Waagenia an<I Waaoeneli.a are preoccupied terras, therefore iireclud- 

 ing this intended expression of e.steein and appreciation for the invaluable service.-^ of Dr. Waahk.n in this 

 department of science. 



