140 DlOTYOSPONGID^. 



nineteen of these and the appearance of the outeiTnost one indicates the 

 margin of the cup. 



There is some variation in the relative proportion of the parts shown in 

 the material at hand. The greatest radius exposed by any specimen is 192 

 mm. ; upon this are nineteen concentric bands ; upon the original specimen a 

 radius (almost but not quite complete) of 147 mm. shows twenty concentric 

 bands. In another example there are fourteen bands in a radius of 100 mm. 

 There is no regular variation in size in either series of bauds, but sometimes 

 there is a slight change in the width of a concentric band ; as, for example, the 

 15th concentric band on the original specimen measures 5 mm. at one place, and 

 8 mm. at another. In three of the specimens the 13th concentric band is 

 situated at a radial distance, measuring its outer edge, of 93 ram., 92 mm. and 

 118 mm. In the first of these the width of this band is 4.5 mm. ; in the second 

 3.2 mm. ; in the third 5 mm. These differences are undoubtedly individual 

 variations. 



The largest example of this sponge yet observed has a greatest diameter of 

 347 mm.; its radius, which appeal's to be complete, is 192 mm. so that its full 

 diameter was about 380 mm. or 15 inches. A smaller individual not complete 

 at the margin has a diameter of 170 mm. 



Geological horizon. In a compact and fine-grained greenish or rusty 

 sandstone from the upper beds of the Chemung group, in the vicinity of 

 Owego, Tioga county, N. Y. Upon one of the specimens are crinoidal 

 segments and abundant examples of Tentacnlites spiculus. 



HALLODICTYA*, gen. nov 

 Sponge growing in an explanate frond without definite limitation of its 

 margins ; in this respect similar to the genera Actinodictya and Crypto- 

 DiCTYA. Surface highly irregular, moulded into circular or elongate nodes 

 irregularly grouped, and broader swellings and depressions. Reticulation of 

 the surface fine, regular and rectangularly developed. 

 Type, Ilallodictya Sdensis, sp. nov. 



Hallodictya Sciensis, sp. nov. 



Plate xxxvi. Fig. 8. 



This very interesting sponge is of considerable size, showing that its 

 explanate mode of growth was maintained in all stages. Its surface is of so 



• This generic term is intended as a partial, though inadequate recognition of the important contri- 

 bntions to the knowledge of the Dictyospongea ol the Chemung group made by E. B. Hall, Esq., of 

 WellsvUle, N. Y. 



