122 University of Texas Bulletin 



Adrianites. Our species has a certain importance on account of being 

 the first one which has been described from American strata. 



Adrianites is much less related to Agathiceras than Mojsisovics 

 and Karpinsky thought. The external suture of the first one is certainly 

 composed of the same simple elements as Agathiceras, but the internal 

 suture of the latter one is as simple as that of Glyphioceras, while 

 Adrianites shows a very well subdivided internal suture. A great dif- 

 ference certainly exists also in the form of' the aperture. Gemmellaro^ 

 has shown that Agath. Suessi has the ventral part of its mouth bent 

 upwards and the lateral portion inward, while a small depression be- 

 tween both produces two lateral prolongations in the form of beaks. 

 In Adrianites the ventral part of the margin of the aperture is convex 

 while on the sides are long prolongations which imitate those of some 

 real ammonites {Oppelia, Perisphinctes). The same difference is in- 

 dicated by the form of the constrictions, which to a certain degree must 

 be parallel to the aperture. Agathiceras shows constrictions bent 

 slightly backward in the ventral part, while in Adrianites these con- 

 strictions in the same place are strongly curved forward. Both genera 

 preserve still the simple ornamentation of the earlier Goniatites, but 

 the development of the other elements, sutures as well as form, aper- 

 ture and length of body chamber, is certainly higher in Adrianites 

 than in Agathiceras. 



I have shown in the description of Adrianites marathonensis nov. 

 sp. that even in specimens where the internal suture is not visible, the 

 genus Adrianites can be easily distinguished from Agathiceras by 

 some features of the external suture. One of these is, of course,, the 

 greater number of saddles and lobes generally, although this difference 

 does not exist in all of the species of Adrianites. Much more impor- 

 tant and characteristic is the form of the siphonal lobe; the two 

 branches of this lobe are always curved and narrow, nearly in the 

 form of a half moon, half as broad as the first lateral lobe, in Adrian- 

 ites; while in Agathiceras they are always broad, nearly symmetrical, 

 and about of the size and width of the first lateral lobe. I have shown 

 that this is persistent in every species so far described of Adrianites, 

 even where the number of saddles and lobes in the external suture is 

 extremely reduced. 



'Gemmellaro, loc. cit., p. 78, pi. 6, fig. 2, 4. 



