Speciks of thk Chemcno Group. 131 



are most prominently developed at the margin, taking somewhat the form of 

 elongated ridges directed toward a common center and hence, here and there, 

 they are to be found extending upon the inferior surface in an irregular and 

 desultory way. The surface of the cup, in the only example in which it is 

 retained, is covered with low nodes or coarse papillae, an-anged with some 

 degree of regularity ; they show, however, no trace of the spicular net-\vork. 

 This specimen is involved in a soft arenaceous shale and these rounded bcxlies 

 on the surface appear to be concretionary, as in places where the rock is 

 exfoliated they show a succession of thin laminae. Probably they have 

 fonned about the projecting points and intersections of the principal spicular 

 strands. 



Dimenfdons. The most complete example observed retains a large 

 portion of the cup which has been bent over so that it lies in neai-ly the same 

 plane with the basal diaphragm. Its entire lengtli is 135 mm. ; its diameter 

 at the upper end, 67 mm.; at the middle, 78 mm.; just above the base, 53 mm. 

 The greatest and least diameters of the base are 70 and 55 mm. Another 

 example preserving the base only, has the major and minor diameters 85 and 

 55 mm. 



This species may be distinguished from T. Edwin-Halli and T. radis liy 

 its different form, extremely nodose and finely reticulate base. 



Locality. In the upper beds of the Chemung group, Wellsville, N. Y. 

 (Collection of E. B. Hall. Named for Mr. John S. Johnston, of Wellsville, 

 in recognition of his intelligent activity in collecting the sponges of the 

 upper Chemung group.) 



THYSANODICryA QTJASILLUM, Sp. HOV. 

 Plate xxxviii, Figs. 3, 4. 



Sponge large and stout ; general form as in the other pjjecies of the genus, 

 with a subcylindrical body slightly expanded above the middle and at the 

 base. The aperture is not well retained. 



Surface marked by large, coarse meshes of somewhat variable size, 

 bounded by distinct ridges which were probably bases of vertical surface 

 lamellae. These quadrules are approximately square, the largest of them 

 measuring about 16x14 mm. These occur about the more expanded portion 

 of the sponge, toward the base the prevailing meshes being somcAvhat smaller. 

 At the intersection of the primary bands there is a noticeable tendency to 

 elevation in the form of low nodes. A faint subdivision of the principal 



