354 ' ^/'^ American Geologist. December, 1902. 
has dissepiments so thin. The name is given on account of the dis- 
tance the apertures are apart in the series. Type in the museum of the 
University of Nebraska, Lincoln, Nebraska. 
Position and locality: Coal Measures; Louisville, Nebraska. 
Thamniscus pinnatus n. sp. 
PI. XXIV. Figs. 3-8. 
Zoarium a flabellate frond varying much in size; one complete 
specimen collected at Roca, is 3 cm. high, and 4 cm. wide ; all other 
zoaria found are smaller and average higher than wide ; the base is 
subcircular from which a stalk ascends to support the frond. The 
main branches (sometimes one branch) ascend in a zigzag manner, 
giving off short pinnae or lateral branches at the bends and bifurcate 
at distances of from 4 to 10 mm. Another form of growth is less 
zigzag in character. It is more like T. octonarius Ulrich, but has 
bee.T pronounced distinct by the author of that species. Branches 
subcircular to subelliptical in section, wider than thick, especially at 
a distance from the stalk, i or 2 mm. in width, more than their own 
diameter apart ; form and size vary in different regions and with the 
condition of growth ; the obverse face is more convex than the reverse. 
The pinnate branches divide with" rounded angles. Pinnae alternately 
places, about 2 mm. apart on each margin of the branch, i mm. 
apart longitudinally along the branches between the bifurcations, usu- 
ally about I to 1.5 cm. long. 
Zooecia increase rapidly in number of ranges, from three, four or 
five, to seven or eight, and infrequently nine between the bifurcations. 
Apertures small, 0.07 mm. in diameter, circular, pyriform in worn 
specimens, arranged in definite longitutinal series, and quite regular 
diagonal series ; fifteen occurring in 5 mm. longitudinally, four and one- 
half in I mm. diagonally; in some well preserved specimens they are 
placed on faint oblique ridges. 
The branches divide with rounded angles, but the ranges of zooe- 
cia separate with acute angles with a wedge-shaped area between. 
Peristome, in perfect specimens, horse-shoe-shaped, elevated, lifted 
into a small spine on each side of the aperture. On the lower side of 
the aperture the peristome widens to wholly or partially surround a 
sub-oval depression which, in perfect specimens, is .14 mm. wide by 
.18 mm. long. 
This species is related to T. octanarius Ulrich, but has more prom- 
inent apertures and a much more diffuse growth. The figures repre- 
sent, two types of growth and what may be two distinct species, yet 
the writer prefers, for the present at least, to place them under the 
same name. One form is less pinnate and more like Ulrich's species. 
Type specimens in the museum of the University of Nebraska, Lin- 
coln, Nebraska. 
Position and locality: Coal Measures: Bennett, Roca and Daw- 
son, Nebraska. Plentifully represented at Bennett. 
