go DlCTYOSPONGID^. 



Prisjiodictya telum, Hall (sp.). 



Platk xvii, Figs. »-10; Plate xxxv, Figs. 7, 8; Plate xlii, Fig. 2. 



1884. DicUjophyton, telum, Hall. Thirty-fifth Ann. Kept. N. Y. State 

 Mus. Nat. Hist., p. 470. 



Sponge small, sharply prismatic, octagonal in section ; prism-faces flat or 

 slightly concave. The base is broad but acute, all the prism-faces being well 

 defined ; the sponge expands rather rapidly attaining its greatest diameter at 

 about one-third of its length, thence it contracts very gradually upward 

 becoming naiTOAvest at about one-fifth of its length from the upper end, 

 again it expands slightly, and at the aperture the margin is somewhat abruptly 

 naiTowed. 



Reticwlwm very fine, without prominent vertical bands upon the prism- 

 faces, but showing, in a few instances, rather coarse hoi'izontal bands. The 

 prevailing large quadrule appears to be that which is bounded laterally by the 

 prism-angles, and it therefore varies in Avidth with the expansion of these 

 faces. These major quadrules are, however, very largely obscured by the 

 finer reticulation of the surface. 



Dimensions. Entire examples of this species are not uncommon. The 

 original specimen, Avhich is an entire internal cast, has a length of 64 mm. ; its 

 greatest diameter is 20 mm. from the basal point and measures 18 mm.; the 

 diameter just below the aperture is 11 mm., and the aperture itself is 7 mm. in 

 major, and 5 mm. in minor diameter. A larger specimen is 87 mm. in length, 

 21 mm. in greatest diameter, and 15 ram. in diameter at the aperture. 



This very neat and pretty species is distinguished by the peculiar cigar- 

 shaped form of the cup and its persistently small size. It appears to be sub- 

 ject to but slight variation in these respects except such as may result from 

 compression or other disturbances in fossilization. Occasionally an abnormal 

 tendency to spiral growth is manifested, and one of the exaniples figured 

 shows how completely this tendency may affect the entire cup. Such a result 

 could hardly be the result of casual cause. 



A block of sandstone from Wells ville is crowded with these sponges, and 

 the exposed surfaces of nearly all the cups, especially of the larger individuals, 

 bear numerous irregularly oblique ridges and furrows, which traverse the 

 cup more or less completely in a spiral direction. In some instances their 

 continuity may be ti'aced more than once around the sponge. In one example 

 these mai'kings are ridges on the surface and grooves on the opposite side, the 

 two being to a certain degree continuous ; the difi"erence in their chai-acter 



