Spfx)ies of the Chkmung Group. 99 



Mode of grointli. The young HydiioceraH tiiheroKum is an anodose, 

 narrowly turbinate cup, in the pi-iniitive stage obcouical and thei-eafter with 

 eight flat or slightly convex sides. The tendency to form nodes is first 

 indicated by low swellings a little distance above the base. At a short 

 interval there is another row slightly more prominent than the firet, but 

 neither of these is sufficient to obscure the plasmatic form of the cup (see 

 Plate vii, figs. 2, 3 ; Plate viii, figs. 1, 2). 



It has been mentioned above that four or five transverse rows of nodes 

 characterize the adult of this species. This statement is intended to refer only 

 to the fully developed nodes, which may be preceded, over tlie ba.sal and 

 prismatic parts of the cup, by one or two rows of incipient nodes ; further, 

 individuals will occasionally bear a subapertural row of low supernumerary 

 nodes. The frequent irregularity in the development of the nodes is due 

 to various causes. A node may fail to appear at its proper place without 

 causing any irregularity in the reticulum (compare Plate ix, fig. 2, where in 

 the two lower rows there is one node wanting, the normal ntimber being filled 

 only in the third row by the abrupt appearance of a full-sized node). Many 

 of these irregularities of development or growth are due to injuries to the cup, 

 which the sarcode of the animal quickly repaired, but the net-work once 

 broken was rarely fully restored to its proper pattern. Figure 2 on Plate vii 

 shows a cup which suffered a rent or break in the net-work at an early stage 

 of development, and this has left its traces in all siibsequent growth. The 

 irregulaiity shown in figure 1, Plate iii, apparently produced by some 

 accident to the cup, has most effectually modified the shape of the sponge. 

 On Plate vii (figure 3), is shown a cup on which, as a result of injury, a 

 node lies in one of the horizontal constrictions and produces a slight deforma- 

 tion, from which the sponge shortly recovered. The disappearance of 

 the nodes towards the aperture may be abrupt or gradual. The apertural 

 surface is moderately broad and smooth, distinctly expanded, and, as shown in 

 several instances, not fringed or tufted on the margin as in the lower Carbo- 

 niferous genus Lebedictta. 



The characters of this species as above given have been chiefly derived from 

 specimens obtained at the locality known as the Brown hill school-house, 

 four miles west of Wallace, Steuben county, N. Y. A remarkable colony of 

 these sponges was there discovered in 1877, when, by the grading of an old 

 road, several hundred specimens of the species were turned out of the super- 

 ficial rock-beds, and since that time systematic operations have produced 

 many more, It ha§ been found that this colony is quite restricted in its 



