32 CARBONIFEROUS AMMONOIDS OF AMERICA. 



more specialized descendants of that type This occurrence, however, is 

 of even greater interest, not as an anachronism, but rather as a forerunner 

 of other forms. Morphologists look to a straight orthocernn ammonoid as 

 the ancestor of the Belemnoidea, but the gap from the Devonian to the 

 Trias has been a rather severe tax on the faith of the geologist. Here, 

 then, we have this gap at least partly filled out by the finding of Bactrites 

 near the toj) of the Lower CarboniferovTS. 



Occurrence. — St. Louis-Chester stage, so-called " Fayetteville shale" 

 of the Arkansas geological survey, on farm of O. P. Goodwin, near 

 Moorefield, Ark. The type was collected b}^ the writer, and is deposited in 

 his paleontologic collection at Leland Stanford Junior University, California. 



Family AGONIATITIDtE. 

 Genus Agoniatites Meek. 



The name Agoniatites was proposed by F. B. Meek" for compressed 

 shells with flattened sides, narrow abdomens, narrow umbilici, with liigh 

 and narrow aperture; septa consisting of f short abdominal lobe, and a 

 lateral lobe consisting merely of a broad curve. The type chosen was 

 Goniatites expunsus Vanuxem. 



Agoniatites opimus White and Whitfield. 



PI. VIL 



1862. Goniatites opimm, White and Whitfield, Proc. Boston Soc. Nat. Hist., Vol. 



VIII, p. 305. 

 19UU. Agoniatites opimus, S. Weller, Kinderhook Faunal Studies, II, p. 121, PI. VII, 



fig. 8: PI. VIII, fig. 1; PI. IX, fig. 1. 



The following description is copied from Dr. Weller's paj^er: 



Shell large, discoid, gentlj' convex on the sides, rather sharpl}' rounded on the 

 periphery. Number of volutions not known, the inner ones embraced by the next 

 outer one to a depth of one-half the diameter of the latter; the umbilicus rather 

 small, but somewhat variable in size, being relatively larger in the larger individuals, 

 its sides rounded. Aperture compressed crescentic in outline, the proportion of 

 height to width about as 7 to 5, the ventral margin sinuate as indicated by the 

 lines of growth. The size of the living chamber not known. Septa deeply' concave, 

 rather distant, being about 2<) mm. apart in the outer volution of a large individual; 



«U. S. Geol. Expl. Fortieth Parallel, Vol. IV, Pt. I, p. 99. 



