Spkciks of the Chemuno Gkoitp. 188 



Thysanodictya iiermenia, sp. nov. 



Plate xxvii, Fig. 7; Plate xxxix, Via. 2 ; Plate xl, Fios. 1-3. 



Sponge attaining large size ; subcylindrical, expanded both at base and 

 aperture. Primary quadrules of the wall of the cup very large, varying some- 

 what in size. These are generally longer than wide and the largest of them 

 may measure as much as 42x21 mm. Such large quadrules generally lie over 

 the median part of the sponge, those toward the extremities being shorter and 

 more nearly square. The finer net-work is retained in places. 



The length of a large specimen, incomplete at the aperture, is 250 ram. 

 Three specimens, two of which were evidently overwhelmed by encroach- 

 ing sediments while growing in their normally erect j)Osition, afford a 

 very clear conception of the structure of the basal plate or diaphragm, though 

 the vertical walls of the cup have been so compressed as to wholly destroy 

 their characters. In the matter of size, they can be compared oidy 

 to 2] quasillmn, whose basal parts have not been precisely made out. 

 Of these specimens one has a diameter of 150 mm., the other measuring to the 

 edge of the peripheral frill, 175 mm., the base of the cup itself being 130 mm. 

 in diameter. 



No other examples of this genus have preserved so distinctly the structure 

 of these basal parts and of these three specimens two retain the reticulum A\-ith. 

 out distortion. Both show that the coarse meshes with strongly elevated 

 spicular margins, such as characterize most other species of the genus, are con- 

 tinued from the lateral walls to the base, and while they present the same 

 general aspect as do those of the upright surfaces of the sponge, their composition 

 is distinctly different. There is no radial arrangement evident in these bands, 

 no center of departure nor apex of attachment. The vertical bands from the 

 lateral walls, bent abruptly into the diaphragm, cross each other from 

 opposite sides, making, over the central portion of the base, large square meshes 

 of the same aspect as those occuring elsewhere, but here formed only by the 

 intersection of the vertical spicular bands. 



The actual crossing of these vertical bands is restricted to the central 

 area of the base ; away from this area and in the peripheral region of the disk, 

 the bands of both sets gradually put on the aspect of the horizontal 

 bands of the cup and actually form such bands. There are but a few of 

 these concentric ridges on the disk, not more than three or four of the first 

 order, and the inner ones are somewhat squared to the quadrate form of the 

 central area, so that the transition from the concentric to the vertical ridges 



