204 University of Texas Bulletin 



border; they are slightly thickened near the umbilical border but do not 

 form real nodules. Between these main ribs other secondary ones are in- 

 tercalated ; they begin above the umbilical border and are a little less strong 

 on the flanks than the main ribs. The ribs are slightly bent forward on 

 the flanks but do not considerably increase in strength. Near the ventral 

 shoulder the ribs show a tuberculiform thickening and from this point 

 bend more strongly forwards ; they end on the ventral shoulder in a strong 

 nodule which is longitudinally prolonged. Between the two rows of nod- 

 ules on the ventral shoulders we observe an entirely flat and smooth zone 

 of the venter ; the ribs do not continue over the ventral portion, but every 

 pair of the ventral nodules is connected by a slight thickening, which pro- 

 duces on the ventral zone a slight undulation. 



The suture is only partly visible. We recognize the external saddle, the 

 first lateral lobe, the first lateral saddle and the second lateral lobe. The 

 suture is not very well preserved because this part of the specimen is some- 

 what corroded, but still we are able to note the general character. The ex- 

 ternal saddle (compare figure) is broad and divided into two parts by a 

 rather deep secondary lobe ; the first lateral lobe is broad and shallow, end- 

 ing in two points, and on the sides are two rather large branches ; the first 

 lateral saddle is higher than the external one, its ramifications are few and 

 simple ; the second lateral lobe is much shallower than the first one, and it 

 is also narrower and trifid. In this specimen the umbilical portion is not 

 preserved but one sees that the second lateral saddle remains rather far 

 from the umbilicus, therefore several auxiliary lobes and saddles must have 

 existed in the intermediate space. 



Figure 1. Metoecoceras aff. whitei Hyatt, suture 



The ornamentation of our specimens coincides perfectly with that of 

 Metoecoceras Whitei Hyatt, only on the ventral part we do not observe as 



