114 CARBONIFEROUS AMMONOIDS OF AMERICA. 



that (le Montfort" used as the type of his genus Afjankks the same species 

 afterwards described hy de Kouinck as Goniatites rotaforhts. Since this 

 genus was described and figured by de Montfort, the laws of priority 

 demand a recognition of it, in spite of the confusion made by later writers, 

 for which he was not responsible. 



Occurrence. — Aganides rotatorbis occurs in America only in the goniatite 

 beds of Rockford, Ind., in the Kinderhook stage. In Europe it is 

 known only in the calcareous shales of Tournai, in Belgium, and in the 

 same horizon in Ireland. Since the species occurs in the same horizon in 

 two widely separated regions, it may be taken as a zone fossil and the 

 horizon called the zone of Aganides rotntorius. Even if the species should 

 not be absolutely identical, there are so many other identical forms in the 

 two regions that the correlation is beyond doubt. Tlie form described by 

 M. Tzwetaev'' as Brancoceras rotator i urn, from the ^Moscow limestone of 

 Russia, probably belongs to another species, although quite closely related 

 to the one under discussion. 



Aganides discoidalis Smith, sp. nov. 

 PI. XXIV, figs. 5-7. 



Shell discoidal, involute, laterally compressed, whorls deeply embrac- 

 ing, and deeply impressedby the inner volution. The height of the whorl 

 is slightly more than one-half of the total diameter, and it is indented to 

 nearly one-third of its height by the inner whorl. The width of the last 

 whorl is nearly one-third of the total diameter of the shell and four-sevenths 

 of the height. The umbilicus is almost entirely closed. The sides of the 

 wdiorl are flattened convex, curving gently to the naiTOw and rounded 

 venter. 



The surface (of the cast) is ornamented only with obscure sigmoidal 

 strife of growth, with a broad, backward-pointing sinus. 



The septa are of the usual Aganides type, with a tongue-shaped ven- 

 tral lobe, deep and rather narrow, pointed lateral lobe, narrow external 

 saddle, and broadly rounded lateral saddle. 



This species is more compressed and discoidal than any otlier known 

 species of this genus. 



«Conchyliologie Syst^matique, Vol. I, p. 30. f"!!^!!!. C!om. G^ol., Vol. VIII, p. 28. 



