26 Calvin on a new Tubicolar Annelid. 
spiral axis never departs horizontally as much as a half tube- 
diameter from the imaginary vertical axis. 
While the worms here referred to were not social, yet a large 
number may be found embedded in a single corallum. Their 
occurrence in the midst of the coral substance, closely and firmly 
embraced by it on all sides, reminds one of the Serpula tubes in 
the Meahdrinas, from the modern i^eefs of Florida and the West 
Indies. The Serpulas that are found associated with Mean- 
drina, however, are attached first to the side of the corallum, 
usually to the surface of a dead portion near the base, and, ex- 
tending upward until they reach the liA ing part, are by the 
lateral growth of the colony enveloped in the stony secretion. 
From the point of earliest attachment, all along up the side, 
the Serpula tube is soldered fast to the corallum. The tube 
may be variously flexed; but the one condition that it must ad- 
here to the surface of some solid body throughout its whole 
length, precludes the possibility of spiral growth. The mouth 
of the Serpula tube, after it is fairly enclosed in the stony se- 
cretion of Meandrina, does not usually advance beyond the sur- 
face of the coral. The growth of the tube and the growth of 
the coral seem to progress with equal step. 
Now it seems to me that the worms that became associated 
with Acervularia at Robert's Ferry could not have been first 
attached to the sides of the corallum, but must have settled down 
among the living polyps on its surface. The embryonic shell 
was attached by its tip or apex, not by its side. The upward 
growth of the coral clasped and held it firmly as fast as it was 
formed. Probably the tube always jDrojected a little beyond the 
surface of the corallum. This would indeed seem to be neces- 
sary in order to afford perfect freedom for the swinging of the 
worm around a vertical axis; a swinging which was necessitated 
by the conditions of spiral growth. 
The worms that infested Acervularia were related in some 
respects to Serpula or Serpulites. The tube is simple, without 
vesiculose walls or internal annulations. It differs therefore 
from the complex tubes that characterize the genus Cormdites 
of Schlotheim, as well as from the small tubes, found in colonies 
on which Nicholson (American Journal of Science, third series, 
vol. iii, p. 304,) founded his genus Conchicolites. Nor is there 
