Species of tiik Chemuno Group. 88 



This species is not completely understood. The original speciine!i, which 

 is an external cast in sandstone ineasurin<' 130 mm. in length, has a diameter 

 of 28 mm. and evinces little, if any evidence of ex[)ansion in the cuj). This, 

 of itself, is the character which will best serve to distinguish the form from 

 related species. The horizontal reticulation of the cup is strong, hut it is 

 probable that its relative prominence is due wholly to mode of pre.servation. 

 A second specimen referable to the species retains a portion of the sponge 

 without compression and in this the prominence of the median vertical band 

 on each prism-face obscures the sharpness of the primary octagonal form of 

 the cross-section, duplicating in some degree the number of prism-fjices. 



A third specimen, though incomplete at both extremities, has a length of 

 200 mm. showing that the species attained considerable length without notable 

 variation in caliber. 



Localities. The original specimen is from the Chemung group of western 

 New York, its precise locality being unknown. Other examples of the sjiecies 

 have been found in the upper sandstones at Wellsville, Allegany county, and 

 at Olean and Hinsdale, Cattaraugus county, N. Y., by Mr. E. B. Hall. 



Prismodiotya PRisMATicA, Hall (sp.). 



Plate xvii, Fig. 1 ; Plate xxi, Figs. 1-6 ; Plate xlii, Fia. 6. 



1882. Dktyophyton fiUtextile, Hall. Notes on the Family Dictyospongidae 



pi. 17, figs. 2, 2a. 

 (Not D.jiUtextile, Hall, 1863 and 1884.) 

 1884. Bictijophyton prismaticum, Hall. Thirty -fifth Ann. Kept. N. Y. State 



Mus. Nat. Hist., p. 469, pi. (17) 18, fig. 2. 

 1889. Dictyophyton prismaticum, Lesley. Dictionary of Fossils, p. 200. 



Sponge regularly enlarging from base to aperture, without rapid increase 

 in diameter at any part ; somewhat variable in shape, often without percepti- 

 ble expansion for a considerable portion of the cup, and with a slightly con- 

 tracted aperture, but usually expanding to an aperture whose diameter is the 

 greatest width of the sponge ; sometimes curved and, not infrequently, some- 

 what twisted ; prism-faces flat. 



Reticulum as in the allied species here described, there being a median 

 spicular band on each prism-face, with two or more accessory bands which 

 may be more or less distinctly retained. The expression of the surface varies 

 with the condition of preservation of the individual specimens, sometimes the 



