CORALS AND BRYOZOA. 
41 
section lenticular, greatest thickness .75 mm. Non-celluliferous space at the 
margin extremely narrow. Cell apertures oval, disposed in longitudinal 
parallel rows, six rows on each face of the branch. Length of apertures, of 
the four central rows, about .18 mm., width .14 mm.; the two outer ranges 
are oblique to the axis and larger than the others; length .40 mm.: margins 
of apertures of central rows sometimes obscure or obsolete. Interapertural 
space elevated, angular, with a row of granules along the middle: margins 
of apertures of outer ranges very thin, but distinct and granulose. Size of 
apertures varying somewhat, from the thickening of the interapertural space 
by silicification. 
This species in some of its features is very similar to Ptilodictya, but it 
differs from that genus in being bifurcate and having an obtusely pointed base. 
This latter feature would exclude it from the genus Stictopoiia, which has a 
thin expanded base, attached to foreign bodies. The specimens of this species 
examined possess the essential characters of Rhinodictya as described and 
illustrated by Mr. Ulrich. 
Formation and locality. Lower Helderberg group, near Clarksville, N. Y. 
THAMNISCUS, King. 1849. 
Thamniscus variolata. 
PLATE XXII, FIGS. 34^46. 
Thamniscus variolata, Hall. Thirty-second Rept. N. Y. State Mas. Nat. Hist., p. 175. 1879. 
“ “ “ Report of State Geologist for 1882. Expl. pi. 22, tigs. 34-46. 1883. 
Zoarium fruticose, several stems arising from a common base, rapidly spreading 
laterally, sometimes forming an infundibuliform frond. Bifurcations very 
frequent, occurring at intervals of from 1 to 3 mm., but seldom more 
than 2 min.; branches clavate, much widened before bifurcation; width 
of a branch variable, but generally about .75 mm. above a bifurcation, in¬ 
creasing to 1.50 mm. On the specimens observed the non-celluliferous face 
is smooth. Cells tubular, apertures circular, diameter .25 mm.; those 
nearest the margin sometimes slightly larger than the others; irregularly 
