HISTORY OF THE EOTIFEEA, OR WHEEL ANIMALCULES. 481 
The family before us* comprises animals which are placed by 
Ehrenberg in nine genera, named Ptygura, CEcistes, Gonoclvilus, 
Megalotrocha, Lacinalaria, Tubicolaria, Limnias, Melicerta, 
and Cephcdo siphon. Each of these genera, however, contains 
but a single species ; and I am much inclined to reduce the 
whole nine to two. Thus, Ptygura, CEcistes, Tubicolaria, Lim- 
nias, Melicerta, and Gejpha losiplwn seem to me to be only so 
many species of one genus ; while Megalotrocha, Lacinularia, 
and Gonoclvilus constitute another. 
To the former of these I propose to appropriate the name 
Melicerta, to the latter that of Megalotrocha. They may be 
distinguished by the circumstance that in the former the indi- 
viduals are always solitary ; in the latter they are (in adult age) 
aggregated by mutual adhesion into somewhat spherical masses 
composed of many animals radiating in every direction from a 
common central point of adhesion. These compound spheres 
are either free or fixed. 
The genus Melicerta, as so enlarged, or the Tube-dwellers 
proper, have the front or upper part of the body capable of 
being turned in upon itself, and concealed with purse-like 
folds, and of being expanded at the pleasure of the animal 
into a disk, which is usually much Avider than the diameter 
of the body. This is either flat or in the form of a very shallow 
funnel. Its outline may form either a simple circle, as in M. 
ptygura and M. ( CEcistes ) crystallina ; two circles united at one 
point, as in M. ( Limnias ) ceratophylli ; or four sinuous lobes, 
more or less developed, as in M. cephalosiphon, M. {Tubicola- 
ria) nccjas, and M. ringens. In each case there is, according to 
Professor Huxley, a double edge to the disk ; of which the 
subordinate one is placed on the under side, and a little within 
the line of the principal. The former is fringed with A r ery 
minute cilia; the latter with long and strong ones, Avliose vibra- 
tile waves form Avell-marked opaque spots which ever run 
along the margin. In each example, e\ r en ivhere the circle of 
cilia is simple and appears in some aspects to be complete, it 
* As I propose to subdivide the class Botifera in a mode differing from 
any as yet published, I add here the technical characters of this family. 
Mclicertadce . — Animal free in infancy, attached in adult age either to some 
foreign fixed body or to others of its own kind ; inhabiting (in most cases) a 
gelatinous tube which is excreted from the skin. Front expanded into a 
broad disk, never five-pointed, but Avith a tendency to form tAVO or four 
rounded lobes, furnished with ordinary vibratile marginal cilia in uninter- 
rupted series. Jaws inclosed in a three-lobed mastax, each malleus soldered 
to the ramus of the incus, and together forming a quadranti-globular mass. 
Body sub-cylindrical, abruptly attenuated to a long, transversely wrinkled 
foot, neither telescopic nor retractile. 
