260 JAMES PERR/N SMITH AND STUART WELLER 



The form is laterally compressed, involute, discoidal, with very narrow 

 umbilicus. The abdomen is narrow, and surmounted by a high narrow hol- 

 low keel, which however is usually not preserved. Where the keel is broken 

 away the abdomen is narrow, less than a millimeter wide, with angular edges. 

 The sides are smooth, devoid of constrictions, ribs, or other ornamentation, 

 so far as could be determined from the casts. 



The septa are complex, ceratitic, with many lobes and saddles. The 

 ventral lobe is long and undivided. The external saddle is rounded and 

 shorter than the laterals. The first lateral lobe is serrated, four-pointed ; the 

 second, four-pointed ; the third, the three-pointed ; the fourth, irregularly 

 three-pointed ; the fifth irregularly bifid. With the sixth lateral lobe begins 

 the auxiliary series of goniatitic lobes, which are of irregular size, and eight 

 in number, growing smaller towards the umbilicus. These characters could not 

 be made out distinctly on Miller's type specimen No. 6208, but the details were 

 clearly seen on specimen No. 6174, from the same locality. The differences 

 between the two specimens, at a casual glance, might seem to be specific, but 

 closer study shows them to be due to difference of preservation, and to different 

 sizes at which the septa are seen. The type specimen shows the keel only 

 at a few places on the periphery, and so indistinctly that Miller overlooked 

 it, while No. 6474. shows the keel, -$% millimeters high, entirely around the 

 periphery. On both specimens the body chamber is incomplete and occupied 

 a little over a quarter of the last revolution. It is not known what was 

 the shape of the aperture, how long the body chamber was, when the keel 

 began, nor what the internal lobes were like, since none of the specimens 

 available sufficed to settle these questions. 



A smaller specimen, No. 6222, from the Kinderhook beds of Burlington, 

 la., showed much simpler septa, and the narrow angular abdomen with the 

 keel broken off. It is undoubtedly in the beginning of the mature stage of 

 growth, and was of value in showing the shape of the cross-section, since 

 both sides were free from the matrix, while in all other specimens one side 

 was fixed to the matrix. 



At present there are known only four specimens of Prodromites gorbyi. 



I. Miller's type, from the Chouteau limestone at Pin Hook Bridge, Pettis 

 county, Missouri. No. 6208, Paleontological Collection, Walker Museum, 

 University of Chicago. This is the type of the genus Prodromites Smith and 

 Weller. 



DIMENSIONS 



Diameter - - - 114""" 



Height of last whorl - 64 



Height of last whorl from the preceding - - 35 



Width of last whorl - 



Involution - - - - 29 



Width of umbilicus - - - 4 



