80 



they are placed. It varies much in its dimensions, differing from T l a 

 to -j-fj- of an inch in diameter. 



The fourth in order is Xanthidium furcatum, or forked Xan- 

 thidium ; a name previously applied to one species by those who have 

 preceded me. It differs from X hirsutum or the hairy Xanthidium 

 in the circumstance that the tentacula are far less numerous, more 

 separated, more regularly arranged, and divergent from the common 

 centre of the animalcule. The tentacula are slender, and gradually 

 tapering to the extremity ; and those apparent around the circumfer- 

 ence are from thirty to forty in number, or even more : what may be 

 the average number on the whole surface of the body, can be only 

 roughly computed ; perhaps from two to three hundred. The aver- 

 age diameter is from -j-^ to -j-^ of an inch. 



The fifth is Xanthidium spinosum, which I so name from the 

 singularly long tapering tentacula which characterize this species. 

 The individuals vary in dimensions, but, upon the whole, measuring 

 in diameter from the extremities of the tentacula, they are the largest 

 of the species of Xanthidia, except the species tubiferum afterwards 

 noticed. The tentacula apparent round the circumference are from 

 fifteen to twenty-five, and they measure in diameter from the -j-^ to 

 ■5-fry of an inch. 



The sixth I have named Xanthidium malleoferum, or hammer- 

 bearing, from the Latin words malleus, a hammer, and fero, to bear. 

 I characterize this (as all the other species) by the form of the tenta- 

 cula, as the only feature by which I can, with any certainty, distin- 

 guish one species from another. The tentacula of this species are for 

 the most part terminated by a small process or arm, placed nearly at 

 right angles, at the extremity of each tentaculum, which nearly bi- 

 sects the little arm, and which thus forms the head of the hammer, in 



two equal parts; thus, or thus, ^j which 



latter is a variety of this species, the two cross aims not forming a 

 straight line at right angles with the tentaculum, but diverging from 

 its extremity at a very obtuse angle. 



The apparent tentacula vary in number from fifteen to fifty, and in 

 length, some being very short, and thickly set round the circumfer- 

 ence, others longer and more scanty, and approximating to one variety 

 of X. ramomm next noticed, having but two instead of three points or 

 processes at the end of the tentacula. The general form of the body 



