58 CLASS I.— ORDER L 



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 

 difier 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. 



