100 
Kirtley F. Mather 
and are flat and parallel to each other. The material at hand 
does not, therefore, differ in any important particular from the 
typical form of the species. 
Horizon and locality. Morrow formation: near Choteau, 
Oklahoma (Station 298). 
BLASTOIDEA 
PENTREMITlDHd 
Genus PENTREMITES Say 
Pentremites angustus Hambach 
Plate III, figures 10-13 a. 
1903. Pentremites angvstiis. Hambach, Trans. Acad. Sci. St. Louis, vol. 
13, p. 53, text figs. 14a-b. 
Chester limestone: Washington County, Arkansas. 
Description. Body conical, more or less elongate and obtuse, 
the length of the ambulacral plates nearly as great as the height 
of the body; base very moderately convex or flattened, basal 
plates small and not discernible in a lateral view in the speci- 
mens with a more flattened base; ambulacral plates about 5 
times as long as wide, ambulacral pores about 17 in 5 mm. ; 
deltoid plates nearly or quite twice as long as wide ; interambu- 
lacral spaces flat or moderately concave, the surface of the plates 
finely striated parallel to their margins, the striations apparent 
only when the preservation is perfect. 
Dimensions of Three Individuals. 
Height 22.7 mm., 21.0 mm., 19.0 mm. 
Maximum diameter 16.5 mm., 18.4 mm., 15.3 mm. 
Length of ambulacral plates 21.0 mm., 19.5 mm., 17.5 mm. 
Maximum width of ambulacral plates 3.9 mm., 4.0 mm., 3.7 mm. 
Length of deltoid plates 9.4 mm., 9.3 mm., 8.6 mm. 
Maximum width of deltoid plates 5.1 mm., 5.1 mm., 4.3 mm. 
Length of basal plates, from center of basal 
attachment scar 4.5 mm., 6.1 mm., 4.2 mm. 
Average number of side plates in 5 mm 17 17 17 
Remarks. Hambach’s material was doubtless obtained from 
one of the limestone horizons of the Morrow group as the ‘Ten- 
tremital limestone” [=Brentwood limestone] of Washington 
County was believed by the Arkansas Survey to be of Chester 
age. 
