2',\S DlCrYOSPONGID^ 



PLATE XX. 



PRISMODICTYA, gen. nov. 



Page 79. 

 (See Plates XVir, XVIII, XIX, XXI, XXVII, XXXIII, XXXIV, XXXV, XXXVI, XW, XLII, LV.) 



Peismodictta cercidea, sp. nov. 



Page 89. 

 (See Plate XLII.) 



Figure 1. An entire flattened, though symmetrical specimen, with subequal 

 extremities. It is possible that the spot at the lower end may 

 represent the aperture and the specimen have thus been drawn in an 

 inverted position, but this is uncertain as the margins of this spot 

 are not so clearly defined as here represented and the other extremity 

 is not fully uncovered. 



Figures 2, 3. Opposite sides of another example which has been obliquely 

 compressed. 

 Chemung group. Wellsville, New York. 



Pkismodictya Allegania, sp. nov. 



Page 84. 



Figure 4. A fragment of a very large individual showing the upward 

 expansion of the sponge, the median division of the prism-faces and 

 the fine reticulation. 

 Chemung group. Scio, New YorTc. 



Pkismodictya speotabilis, sp. nov. 



Page 82. 



Figure .5. A nearly entire specimen representing a fine sponge, which attains 

 its greatest expansion shortly above the base and is regularly pris- 

 matic for the rest of its extent. The prism-faces are not developed 

 near the base of the cup, although thus represented in the lithograph, 

 but the surface about the apex is smooth and round for a consider- 

 able distance. 

 Chemung group. Wellsville, New Yoi^h. 



Pkismodictya pakallela, Hall (sp.). 



Page 82. 



Figure 6. Transverse section of an uncompressed specimen. 



