.78 SUPPLEMENT , 



animal, whose anus is always terminal and posterior, and 

 which, besides, has no sort of adherence with its tube. 



The genus Serpula may be thus characterized : animal 

 moderately elongated, a little depressed, composed of a great 

 number of articulations very much crowded, consisting of an 

 abdomen and cephalothorax, tolerably distinct ; the head, or 

 first segment, is larger than the others, and has for appendages 

 above a pair of elongated tentacula, dilated into an operculi- 

 form disk, radiated at the extremity, and one of which alone 

 is completely developed. On each side is a tolerably large 

 gill, in the form of an unilateral comb, composed of a variable 

 number of long cirri, furnished with a double internal rank 

 of mobile barbs ; the thorax is short, with a sort of membrana- 

 ceous sternal plate inferiorly ; the appendages of the thoracic 

 and abdominal rings are divided into two oars, the upper one 

 provided wath a fasciculus of subulated setae, returning to- 

 wards the back ; the lower with a range of hooked setse, for 

 the thoracic rings, but the reverse for the second. The testa 

 is in the form of a conical tube, solid, entirely calcareous, irre- 

 gular convoluted, free in a portion of its termination, and fixed 

 by its summit ; the aperture is rounded. 



The characters just assigned to the genus Serpulas, after the 

 most common European species, will suffice to make known 

 the general form of the animal, and all that presents itself ex- 

 ternally in relation to it, adding, however, that it is contained 

 in a membranaceous envelope, as are all the tubicolse— an 

 envelope which, without doubt, produces the shell, always 

 much larger than itself. As to the organization of these ani- 

 mals, it has been very little studied. 



The intestinal canal commences by a buccal orifice, alto- 

 gether anterior, provided with two lips, without any trace of 

 teeth or proboscis. This orifice conducts into the intestinal 

 canal, which proceeds directly to the anus, is always mem- 

 branaceous, and even presents no very distinct gastric en- 



