326 BALAN1DJE. 



times both rami are short and blunt. Some of the segments 

 in the third cirrus often support very coarsely and doubly 

 pectinated spines. Under the head of T. porosa, it will be 

 seen to what a remarkable degree the relative numbers of 

 the segments in the several cirri vary, even in specimens 

 taken out of the same cluster. 



The Branchiae are well developed (at least in T. porosa 

 and costata), as a large, plicated, tapering fold, with a small 

 second fold on the inner side at the base. In T. porosa the 

 stomach is destitute of caeca. The vesiculcB seminales in 

 this same species are large, with their broad, blunt ends 

 reflexed. The ovarian tubes surround the sack, and cover 

 the basal plate. 



Distribution and Habitats. — This genus is confined to 

 the tropics, and to the warmer parts of the temperate seas : 

 in the southern hemisphere, it ranges south, to the Cape of 

 Good Hope and to Van Diemen's Land: in the northern 

 hemisphere it does not appear to range so far; I do not 

 know of any authentic case of a species having been found 

 in the Mediterranean, or on the shores of the United States, 

 north of the West Indies. Tetraclita porosa is found round 

 the whole world ; T. radiata, also, has a very wide range, 

 inhabiting the West Indies, the East Indian Archipelago, 

 and New South Wales. This latter species, as well as 

 T. ccerulescens, is often attached to the bottoms of ships, 

 adhering to Balanus tintinnabulum. The several species 

 live attached to tidal rocks, to littoral shells, or to massive 

 corals. I have met with two instances, in the West Indies 

 and the Philippine Archipelago, of T. porosa adhering to 

 wood. Tetraclita porosa seems to feed chiefly on crustaceans: 

 the number and the size of the amphipods, isopods, and 

 entomostracans, together with an annelid, in the stomachs of 

 some specimens from South America, was quite surprising. 

 As many as five species occur in the same region, in the 

 eastern half of the world ; thus on the shores of New South 

 Wales, we have T porosa, vitiata, radiata, picrpurascens, 

 and rosea ; in the Philippine Archipelago, we have T. porosa, 

 vitiata, costata, and ccerulescens. 



I have not seen any species of this genus fossil. 



/ anatiun. — The species vary in shape nearly, but not 



