134 DiCTYOSPONGID/E. 



is barely noticeable on a cursory inspection. The character of this peculiar 

 reticulation is such that four small wedge-shaped areas remain, one in each 

 quadrant, where rectangular reticulation can not occur. These are at the 

 sides of the broad bands of vertical spicules extending over from the lateral 

 walls of the cup, and here the net-work is not only irr-egular but seems to 

 have formed a node or tuft. 



Beyond the edge of the basal plate extends a frill of considerable %vidth, 

 very sirailiar in character to that occurring in Phragmodictya catilUformis, 

 but not as wide as has been observed in that species, and with a crenulated or 

 deeply furrowed surface. At the union of the frill with the body of the 

 sponge, low, irregular and elongate nodes are formed, as observed in other 

 species of the genus. The more prominent of these extend outward from the 

 periphery over the lower surface of the expansion and may become consider- 

 ably elevated, with smooth, concave interspaces. The coarse reticulation of 

 the skeleton is here visible only near the base of the frill, further outward 

 the net-work being obscured. In the specimens under consideration the 

 actual extent of the frill is pretty clearly defined by a discoloration of the 

 matrix. 



The strong, coarse net-work of the basal disk does not obscure the 

 exceedingly fine ultimate reticulation which is everywhere seen. In one 

 of the three specimens oblique compression has disturbed the regularity of the 

 basal net-work, but the strong irregular nodes at the periphery are very 

 pronounced. Confirmatory evidence of the view that these convex plates 

 are basal and not apertural like the sieve-plate in Euplectella, is the follow- 

 ing fact ; The arenaceous slabs of the upper Devonian of western New 

 York frequently have their surfaces covered with various forms of wave 

 and ripple marks and furrows left by the dragging of pebbles, tracks of 

 crustaceans, etc. Such surface markings were made on the soft muds 

 which subsequently became shales, while the encroachment of more sandy 

 sediments produced relief impressions of these configurations so that such 

 reliefs are found upon the lower side of the sandy layers. One of 

 these basal disks of Thysanodictya liermenia lies at the upper surface 

 of such a sandy slab, its convex face downward, the compressed cup above, 

 while the lower surface of the slab is covered with relief impressions of 

 mechanical markings made upon the sediments immediately beneath. 



Locality. In the upper beds of the Chemung group at Hinsdale, Cat- 

 taraugus county, N. Y. (Collection by E. B. Hall.) 



