58 
CLASS I.— ORDER I. 
semble military casques, and are placed on the bor- 
ders of the cells, which they appear wholly to 
close ; they are sometimes wanting, nor is it rare to 
find Polypidoms entirely deprived of them. Various 
have been the opinions respecting their purpose : I 
am inclined to consider them as ovaria enclosing the 
germs of future individuals; having observed that 
these vesicular bodies are sometimes whole, and in 
this case I have always found them filled with small 
globular bodies. It appears that these ovaria open by 
a transversal slit; whenever this is met with, the 
ovaria are found empty. 
The Acamarchis resemble each other in form ; they 
differ by the number of the teeth that are placed on the 
external side of the cells, and by the form of the latter, 
whose border is either smooth or toothed : the upper 
membrane of the cells is frequently wanting, and it 
was in this state that Ellis figured his first species. 
The substance of the Acamarchis is more horny 
than cretaceous. 
Their colour is a dull green, or greyish, which 
changes to a fawn, more or less bright, by desiccation, 
or exposure to air and light. 
Their size never exceeds a decimetre, and is usually 
much less. 
They attach themselves by numerous fibres to solid 
marine productions ; they are found in the equato- 
rial and temperate seas of either world. 
NERITAL. 
1. Acamarchis neritina . A single tooth on the 
external side of the cells. —Plate 3. fig. 2. a. B. 
Mediterranean. 
