ORGANIC DEPENDENCE AND DISEASE 
85 
erto in the Cambrian, occasional in the Ordovician, more 
common in the Silurian, they became abundant and wide- 
spread in the Devonian and thence onward to the present 
fauna and their activities now are known not to be confined 
to the salt waters only . 1 
Sponges. Excavations which seem referable to the activ- 
ities of perforating sponges of types comparable to the liv- 
ing Clionaand Thoosa, which 
are familiarly known to bore 
in calcareous remains, have 
been observed by us in va- 
rious brachiopod and acepha- 
lous shells of the Devonian. 
Our record of them does not 
extend into the earlier fau- 
nas. We are holding the same 
reservation regarding the 
precise nature of some of 
the borings here assigned to 
sponges of this type because 
of want of full comparative 
evidence, but the assignment 
is based on comparisons of 
size and mode of growth as 
between the microscopic tu- 
bules of the algae and the large regular tubes of the worms . 2 
In a previous discussion of such perforating organisms 3 we 
instituted the generic designation Clionolithes for a group 
which was based on the form described by McCoy 4 from 
1 See T. S. Collins. “Some Perforating and Other Algae on Fresh Water 
Shells”; Erythea, v. 5, p. 95. 1897. 
2 Comparison with the tubules of living perforating sponges may be made 
by reference to the work of Emile Topsent in the Archives de Zoologie Experi- 
mentale, 2d ser., v. 5 bis, 1887, 1891; 4th ser., v. 7, 1907. 
3 i 1 Dependent Life. 7 7 
4 “ British Paleozoic Fossils, 7 7 1855, p. 260, pi. 13, fig. 1, la. 
Fig. 69. Boring algae in the test of 
the trilobite Odontocephalus selenn- 
rus (Devonian), x 25. 
