n:ii.onn i 



al com -uh^eneric name- ha\e lieen applied to these later foi 



f>,/ (l ;i/,i,vy/i-i/;/v. where the frontal linili of tin- cephalon heard a row of inci-or-like 



in which similar processes extend to the genal alible-; 

 jidiiim ha- an ediinute margin ami it- posterior extremity 



cted into a -emidrcular collar. The-e names are taxonoinically snlionlinate 

 in the third degree term />/,'/// initf<; that is to -ay. we that they 



all, with the inclusion of those iMvonia 1 ; - referred to above as "Chastnops" 



(forming a homo! ip) are fulxidiary to a diruion whote diagnostic feature 



i- the more or If-- omjilcte coalescence of the. first and second lateral ^labollar 

 lolies, ami for Mich a >nl>^oncric livi-ion ;i designation is needed (e. g.. Synph< : 



typical cxpros-ion and phylctir nonnai of lt<il>nniti-s is represented by a 

 series of upper Silurian and rarlir-t l'c\onian form-, in wliich the ^lalidhir location 

 i- i" ml the py^i'li'im caudate. An excellent example is the D. liinuliiriin 



<Jreen. < .i-ara L'roup. This type is foreshadowed in the lower Silurian hy 



/'. a. /(./.> Millings, of the Trenton limestone, and perhaps by l>. carlnji Meek, of the 

 Hnd-on Itiver tfroup. . .'/-x /.-//f7/>- still maintains the t'arial suture of 1'tenj- 



ij'im- . ith the complete ^laKellar lol.ation. anterior width of glabella and 



ariiminate iiy^'idium of typical l^ilmnnitcs. 



The acmic or mature type uf I>>itin<init<< becomes simply ornamented l>y 



ate processes on the cephalon. lioth in the later (Waldroni Niagara ( /'. 

 Hull', and in the Lower Helderberg (D. n'i<nfn* Conrad, D.lrl<l-n Hall), or may 

 ha\f -hint triangular spines extending partially or fiitirely about the margin of the 



alon(/< n-rett. /'./<//;///< 'larke). With the close of the Lower Heder- 



the tyi>e seems to have abruptly disup[ieurcd. but it reappeared in the Hamilton 

 fauna devoi.l of other dermal ornament than the broad. Hat marginal exten-i" 1 

 the pyL'idium. <*. This i> the last of the race in American faunas. 



These appear,! :. to be interpreted and summarized as 



follows: The lobal coalesenee of the lurian sped.-. /' ' '//. trooxti. /'. 



.dive of immature or epacmic developn 1 lie relation of 



I/". -e ami probably al. A ftei passing the acmic 



"d. when phyl- iity manife-t- itself in the variety and extravagance of 



the dermal ornamentation, tli' on to the epacmic condition of lobation i- Imt 



an accompaniment of the decline of the 



metopux :it- but a secondary stage in thi- process, a stage i 



advanced than that indicated by I>. >' . I5ut in eertain - mi-, 



there i- a lateral e\pan-ion of the tir-t and .-econd ^lubellur ' iving to the 



L'lal>ella as a whole a -omewhat ^lol.. ?. I'mm -udi gp< *he point of 



