122 Trans. Acad. Sci. of St. Louis. 



chamber not known. Septa deeply concave, rather distant ; 

 being about 20 mm. apart in the outer volution of a large 

 individual ; the sutures forming a low saddle upon the umbil- 

 ical angle, then gently curving backward and forming on 

 each lateral face a single broad lobe which occupies the entire 

 width of the volution; the direction of the suture upon the 

 periphery cannot be certainly determined, but there seems to 

 be a low saddle on either side, with a shallow ventral lobe 

 between. Position of the siphuncle unknown. Surface 

 marked by very faint lines of growth which are sinuate on 

 the periphery of the shell. 



Remarks. In the original description of Goniatites opimus, 

 specimens of two entirely different species were apparently 

 used, the general form of the shell being described 

 from one specimen, and the suture from another. 

 The specimen here illustrated on plate VII, figure 8, is 

 the type of the species in the University of Michigan 

 collection, and corresponds with original description of the 

 general form and proportions of the shell. This specimen, 

 however, does not preserve the suture, and the original speci- 

 men from which the suture was described has not been 

 seen. This latter specimen was probably a fragmentary one 

 not preserving the form of the shell, which was be- 

 lieved to belong to the same species as the type which has 

 been preserved. In the collection received from Prof. 

 Calvin there is a goniatite much larger than the type 

 of G. opimus but agreeing closely with it in its general 

 form and proportions in all respects save in its relatively 

 larger umbilicus. This specimen is illustrated on plates VIII 

 and IX, and it is believed to be an individual of the same 

 species as the type of G. opimus; but unlike the type speci- 

 men several of the sutures are fairly well preserved, and are 

 entirely different from the sutures of G. opimus as indicated 

 in the original description. It is therefore probable that the 

 suture originally described as that of G. opimus is really the 

 suture of some shell which is not only specifically, but gen- 

 erically, distinct from G. opimus. The true suture of the 

 species is in all respects that of the genus Agoniatites, and 



