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 Stictopora, which has a 

 thin expanded ba.se, attjiched to foreign bodies. The specimens of this species 

 examined possess the essential characters of Rhinouictva as described and 

 illustrated by Mr. Ulrich. 



Formalion and locality. Lower Helderberg group, near Clarksville, N. Y. 



THAMNISCUS, King. 1849. 

 Thamniscus variolata. 



PLATK X.XII, FIGS. 3<-16. 



Thamniscus variolata. Hall. Thirty-second Rept. N. Y. State Mus. Nat. Hist., p. 175. 1879. 



Report of SUte Geologist for 1882. Expl. pi. 22, figs. 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 mm.; branches clavate, much widened before bifurcation; width 

 of a branch variable, but generally about .75 ram. 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 



