CORALS AND BRYOZOA. 31 



infrequent. Apertures broadly oval, sometimes nearly circular, length .33 

 mm., width .25 mm. ; irregularly disposed, frequently in contact. Anterior 

 margins thin, very slightly elevated; posterior strongly elevated, oblique; 

 sometimes with two slight denticulations, which give to the aperture a sub- 

 trilobate form. Surface marked by maculae, the centers of which are distant 

 from each other about six mm. ; the apertures immediately adjacent are larger 

 than the others, more oblique and radiating from the maculae. Interaper- 

 tural space smooth or vesiculose. Intercellular space vesicular ; vesicles 

 irregularly arranged, many of them, comparatively, very large. 



The surface of this species presents a variable appearance, according to the 

 degree of weathering. 



Formation and loralities. In the shaly limestone of the Lower Helderberg 

 group, at Cat.skill, and near Clarksville, N. Y. 



LiCHENALIA TORTA. 



PLATE XV, FIGS. 1-5, 7. 



Liehenalia torta, Hall. Thirty-second Kept. N. Y. State Mus. Nat. Hist., p. 157. 1879. 

 In part LidienalUi ti>iia,'ll\u.. Rejiort of State Geologist for 1882. Expl. pi. 15, tigs. 1-7. 



ZoARiUM consisting of lamellate expansions; sometimes flat, at other times more 

 or less involved and contorted. Under surface a thin epitheca marked by con- 

 centric wrinkles and striae, with fine radiating striae. When the celliliferous 

 tissue of the bryozoum has been removed, the radiating striae on the upper sur- 

 face of the epitheca are very sharp and prominent, and at their junction with 

 the concentric striae form minute nodes. Cell apertures broadly oval or circu- 

 lar, sometimes sub-triangular or trilobate, diameter .30 mm. ; space between 

 adjacent apertures equal to, or less than, the diameter of an aperture. 

 Anterior margin slightly elevated, posterior side strongly elevated, with two 

 slight denticulations. Surface with slightly elevated monticules, 



Formation and localities. Lower Helderberg group, near Clarksville, and at 

 Schoharie, N. Y. 



