-i MI -A 



Pralowartkl* ab 



.loiil.t of tin- rorrectti.'-- nf inn identitiratimi. nor of tin- -perilir identity of a large 

 proportion of the -pei-mien- th;it American authors generally and erroneously place 

 under Sowei by'- Ii,llfi;>i>li<mliilt><itii.<ii\i<\ I //</. The only difference between 



the two supposed species mentioned by Hall is that one has a cancellated surface, 

 the other not According to our view tin* difference is merely a matter of preserva- 

 tiou. ami if we are correct in this then /'. <>///(//( is the commonest by far of all 

 the Ix)wer Silurian bellerophontids. 



o /'. bilobata Sowerby, the original figures of which are reproduced on page 

 869, we have not the least doubt that it is specifically distinct from P. cancrllulu, 

 that species being a larger and more globose form. Indeed, we doubt very much 

 that Sowerby's species occurs in America. 



Formation and lotalUy. Hot uncommon in th>> Hl:u-k Klvcr group, principally In the Ctenodonta 

 bed. at Mlnm-.r I'aul, Canonn Fulls, Chattleld and other ltx-al!ti<> In Minnesota. Also In Mercor 



r.ninty, K.-ntii'-k> . and In Canada. It is very aVfcndant In the Trenton, Utlca, Loralne, and Richmond 

 ttroiip*, in th.-ih-t ihr.-v especially, at numerous localities In Minnesota, Wytontln, Iowa, Illinois, K.-n 

 lucky, Ohio, Indiana, Tenneuce, New York and Canada. 



PBOTOWARTHIA SUBCOMPKESKA, n. sp. (Ulridi.) 



I'LATK I.XIII. KI08. ~U. 



II large, compressed-subglobose, the greatest bight and width about as six 

 is to four; back broadly rounded, sides somewhat flattened, umbilicus closed, 

 wanting; aperture semi-ovate, outer lip thin, inner lip moderately thick and reflexed 

 in the umbilical regions; callosity extending over the whole front of the inner 

 volution, apparently smooth; sinus broad and about as deep, the depth decreasing 

 slightly with age; apertunil lobes rounding very gently to the sinus where the 

 outline makes a rather sharp curve. Surface marked by fine lines of growth and 

 near the aperture by some obscure wrinkles. The callosity which extends over the 

 inner volutions exhibits the usual fine irregular revolving lines in the umbilical 



I!-. When the shell is removed, the cast shows a narrow furrow down the 

 center of the bark and several more faintly on each side. Greatest diameter 41 

 mm.; smallest diameter 'J'.t mm.; width of aperture 27. "> mm.; bight of same (central) 



mm.; width of inner volution K! mm.: depth of -inus 7 or 8 mm. 



This fine species, besides attaining a greater si/.e than /'. <-nn<-i-ll,iiii, differs from 

 it in being narrower and in wanting. - known, the delicate revolving line- 



of that species. The umKiliral callo-ity of the inner lip i- also less and does not 

 slope outwardly, the edge only being reflected. Ilrllcrophon tnnrruii-ensi* Miller and 

 Iyer. whirh also may belong to Protoii-'irthin, i> in-utliciently known. According to 

 the descriptions, it seems to differ in having the dor-al -i'lr -h.trply angular. /'. 

 pltinodorsata has a wider aperture, revolving lines, and a flat dorsum. 



