Fauna of the Morrow Group 
136 
Remarks. In its mode of branching this form resembles R. 
persimilis, of the Chester group, but may be readily distinguished 
from it by its more robust form. The appearance of the tubuli 
along the interspaces between the vestibules will readily serve 
to separate this species from others of the genus. 
Horizon and locality. Morrow formation: near Ft. Gibson, 
Oklahoma (Station 301). 
Rhombopora attenuata Ulrich 
Plate Vh figure 10. 
1890. Rhombapora attenuata. Ulrich, Geol. Surv. Ill, voL 8, p. 655, pi. 
70, fig. 7. 
Keokuk group: Warsaw, Illinois. 
1894. Rhombopora attenuata. Keyes, Mo. Geol. Surv., vol. 5, p. 34. 
Keokuk limestone: Warsaw, Illinois. 
Description, Zoarium a slender stem, 0.6 to 0.9 mm. in diam- 
eter, branching dichotomously at unknown but doubtless com- 
paratively remote distances, Zooecial apertures arranged reg- 
ularly in longitudinal and diagonal series, the former the more 
obvious. Apertures oval, opening into an elongate vestibule 
typically hexagonal in outline, due to the truncation of the 
rhombic area at either end; about 16 apertures in 5 mm. longi- 
tudinally. Interspaces moderately thin, acutely ridge-like, orna- 
mented with a single row of very small and closely-set nodes 
along the summit; the nodes at the junction angles commonly 
somewhat larger than the others. 
Horizon and locality. Morrow formation: near Ft. Gibson, 
Oklahoma (Stations 296 and 301). Kessler limestone: East 
Mountain, Fayetteville, Arkansas (Station 209). 
CYSTODICTYONID^ 
Genus CYSTODICTYA Ulrich 
Cystodictya brentwoodensis n. sp, 
Plate VI R figures 1, la. 
Description, Zoarium consisting of bifoliate branches, elon- 
gate elliptical in cross-section, dividing dichotomously at inter- 
vals of about 10 mm. and varying in width from 3.2 to 3.5 mm. 
with an increase to as much as 6 mm. immediately before bifur- 
cations. Zooecia in moderately definite longitudinal series. 
