86 CARBONIFEROUS AMMONOIDS OF AMERICA. 



Foord and Crick, in (}. lisieri, bnt these three differ in septa, in involution, 

 and shape of the whorl, G. listen being intermediate between the others, 

 and no transitions from one to the other being known. 



Occurrence. — Gasfrioceras carhonarium is characteristic of the middle 

 division of the Coal Measures in England, Belgium, and Germany. In 

 America it has been found at the same horizon in western Arkansas — Scott 

 County, near Boles — associated with G. Jistcri. The identification is not 

 beyond question, on account of the nature of the preservation of the speci- 

 mens. It is therefore referred with some doubt to G. carhonarium. Figured 

 specimen deposited in the geologic collection of Leland Stanford Junior 

 University. 



GrASTRIOCERAS COMPRESSUM Hyatt.- 



PI. IX, figs. 1-3. 



ISHl. Gastrioceras com;p7'i'Ssuin, A. Hyatt. Second Ann. Kept. (tpoI. Sur\-. Texiis. 

 p. 3.55, figs. 57. 5S. 



The following description is quoted from Hyatt's paper: 



The form of the whorl is helmet-shaped, and at the diameter of 109 mm. in ti 

 cast the greatest transverse diameter was 42 mm. ; the distance in a straight line from 

 umbilical shoulder to center of abdomen, .38-.39 mm. ; the abdomino-dor.sal diameter. 

 23 mm. The increase hy growth in both diameters is slow and the umbilici conse- 

 quently shallow. The involution covers more than two-thirds of next internal whorl 

 at the diameter of 10'.> nun., and in another specimen at diameter of (3S nun. it is just 

 two-thirds. The still younger whorls are numerous and visil)](> from the sides at tlic 

 centers of the umbilici, and doubtless the amount of involution is corre.spondingly 

 less. Constrictions appear in the smaller specimen measured and in the younger 

 stages of another flattened example. 



The ventral lobe is divided h\ a large bottle-shaped siphonal saddle divided b}- 

 a siphonal lobe at the exti'emity; the lateral branches of the ventral lol)es are very 

 long and acutely pointed, as are also the first lateral lobes, which are of the same 

 length as these branches of the ventral. The first lateral saddles are hastate and 

 acutely pointed, and second lateral saddles are. as is usual in this genus, subhastate. 

 The inner outlines of these last are concave near the points, then suddenly convex 

 internally where the lobe of the umbilical shoulder begins. These last-mentioned 

 lobes are also acutely pointed, but nuich more abbreviated than the other two pairs. 

 The shell is strongly striated, Ijut it is not pilated or otherwise marked, except when 

 constrictions occur. 



Occurrence. — Lower Carboniferous, St. Louis-Chester stage, Bend for- 

 mation, San Saba Count)^, near Bend, Tex. The type is deposited in the 

 U. S. National Museum. 



