22 BULLETIN : MUSEUM OF COMPAKA.T1VE ZOOLOGY. 



ber of spicules peculiar to itself that were rarely or not at all found in 

 the other nodules. The Monactinellids, especially Figure 7, were found 

 in nearly all the slides, and I think Figure 7 was found in every nodule 

 examined. Knowing the destructive effects that even a slight friction 

 of these among one another would have on the delicate barbs, we must 

 conclude, it would seem, that these spicules have never been moved, but 

 have been developed on the spot where they are found. Some of these 

 globo-stellates that are broken may have been carried from surrounding 

 sponge beds and broken up on the road, but, as these occupy the outside 

 chiefly, it is easily seen that such movement and consequent breakage 

 would be a natural result. It therefore seems to me that this study is 

 a confirmation of the view taken by Professor Sollas that the flints result 

 from the continuous growth of sponges in situ, and that the presence of. 

 the minute spicules so perfectly preserved, and which he did not find, 

 furnish the strongest proof. I must dissent, however, from his other 

 conclusion, that the nodules are replacements of chalk by siliceous solu- 

 tions deposited in the interstices. 



In the Texas flints there are comparatively few of the chalk-forming 

 organisms found fossil, and these are so isolated that they seem to have 

 no connection at all with one another. It is reasonable to suppose that 

 they may have fallen into the framework of the sponge and sunk down 

 into the siliceous mass on the death and decay of the sponge body. In 

 one nodule there were four concentric rings of chalk followed by as many 

 of silica on the outside of the nodule. The chalky material was silicified 

 but not replaced, and it is but reasonable to suppose that such would 

 have occurred within the nodule had the nodule been formed by the 

 replacement of the chalk as Professor Sollas proposes for the nodules of 

 the English flint. Therefore, in consideration of the above points, I have 

 thought it allowable to suggest that each nodule represents a separate 

 sponge bed, in which many generations of sponges have lived and died 

 in all stages of development. On the death of any certain part, the spic- 

 ules fell away, many of them down below into the mass at the bottom. 

 Here the process of solution went on continually, and nearly all the spic- 

 ules were dissolved and few left in the dissolved mass. Why so many 

 of the dermal spicules are left and the zone spicules nearly all dissolved 

 is hard to account for, and I have no explanation to suggest. Many of 

 the spicules would doubtless fall outside of the growing mass, and these 

 might be dissolved according to the method suggested by Dr. Wallich 

 elsewhere quoted, and by movement through the water settle around 

 the masses already dissolved, and thus form the concentric rings above 



