H1PPOTHOA. 295 



"This species differs so decisively from the two pre- 

 ceding, that there can be no doubt of its being specifically 

 distinct. The cells are calcareous ; enlarged, and rounded 

 at the distal, and pointed at the proximal end. Their 

 direction is linear; they are attached to each other at their 

 extremities, and their length is about four times their trans- 

 verse diameter/' (JR. Q. Couch.} 



4. HIPPOTHOA CASSITERIDES, Couch. 



Hab. " On a stone betwixt the Scilly Islands and the 

 Land's-end." "The cells are stouter and more pear-shaped 

 than in H. divaricata, and the threads of connection shorter 

 and stouter/' "At a short distance from the proximal 

 lip is a small pearly tubercle, which is larger in one cell 

 than another/' " This tubercle is very different from any- 

 thing ever observed in H. divaricata, and constitutes it a 

 distinct species/' (R. Q. CoucL) 



Genus XI. GEMELLAEIA, 



Gen. Char. Polypidom plant-like, sub-calcareous, rather soft 

 and flexible when dry, much branched dichotomously : cells 

 geminate, exactly opposite, united back and back with a thick 

 dissepiment, a joint above and below each pair. Polypes Asci- 

 dian, with elongated tentacula ; no gizzard. Dr. Johnston. 



