6 MARINE POLYZOA. 



In the third subdivision of the Catenicellce, or that here termed 

 " Simplices," there is at present but one species. This differs so 

 much in many respects from any of the former, that it might, 

 perhaps, constitute the type of a distinct genus : agreeing how- 

 ever as it does, in essential particulars, with the rest, it has been 

 thought better to place it, at least provisionally, with them. In 

 this form there are neither "fenestrae" nor "vittae," nor are there, 

 properly speaking, any avicularia. The latter, however, are repre- 

 sented by two strong lateral processes, which are grooved in front, 

 and may in the living state have a moveable member, either man- 

 dible or seta, which is wanting in the dead specimens. 



#. Fenestratae. Cells fenestr ate in front ; ovicells terminal. 



Catenicellae fenestratae, Busk, in Macgillivray's Voy. Rattlesn. 

 i. 352. 



1. CATENICELLA LORICA. PI. I. 



Cells elongated rhomboidal, truncate at each end. Fenestrae 

 3, large, the lowest the largest. Avicularia large and strong ; 

 back marked with faint longitudinal striae. 



Catenicella lorica, Busk, in Voy. of Rattlesn. i. 358. 

 Hob. Bass' Strait, 45 fathoms. 



Colour white, transparent. A fine, widely-branching species, 

 in which the catenulate aspect is more evident to the eye than in 

 almost any other. It is at once recognizable by the rhomboidal, 

 scutate form of the cell, viewed anteriorly; and when the back is 

 also vie\ved, the resemblance of the two aspects to the back, and 

 breast-plates of a coat of mail, is very striking. The structure of 

 the lateral processes is more distinctly to be made out in this spe- 

 cies than in any other. Each lateral process consists, 1. of a 

 deep cup-like cavity above ; 2. a middle compartment the avi- 

 cularium; and 3, a third loculament below the avicularium, the 

 wide opening of which is covered in by a convex transparent mem- 

 brane. The bottom of this loculament appears to be perforated ; 

 and it is to be noticed also, that there is a small central perfora- 

 tion in the septum separating it from the cavity of the avicula- 

 rium. Towards the bottom of the cell, on each side, is a well- 

 developed lateral area, of exactly the same conformation as the 

 subavicularian loculament, and like it covered in by a convex 

 transparent membrane. It might be supposed that these cavities 

 were for the purpose of containing air, in order to render the 

 otherwise heavy branches of the polyzoary buoyant. They at all 

 events appear to be perfectly empty. 



