ARTICULATA. 101 



has its extremity enlarged into an operculum for closing the aperture. The 

 tubes which these animals secrete are calcareous, and twisted in a very 

 irregular manner. They are affixed" to submarine bodies, either singly, or 

 a great many in a single mass. The tubes are common in tlie tertiary and 

 secondary formations. 



Fam. 2. Ainphitritidce. In this tamily the indistinct liead is composed 

 of three segments, the thorax of not less than twelve, and the abdomen of a 

 o-reat many. The mouth has numerous prehensile tentacular filaments, 

 and the tube is formed out of a mucous secretion to which extraneous 

 objects, such as fragments of shells, are affixed. They live singly or 

 aggregated. Amphitrite {pi. 77,/^. 13), Sabella [pi. 75,fiff. 68), Terehella 

 ipl. 76, fig. 82). The genus Hermdla resembles the Dorsibranchia in 

 having the branchiae dorsal ; the cephalic appendages not being branchia? 

 but tentacles, according to Milne Edwards. 



Class 2. Cin'hopoda. 



The animals of this class are monoicous, inclosed in a hard shell or 

 subgelatinous envelope, deprived of locomotive powers, and affixed to 

 extraneous submarine bodies, some by a peduncle {pi. 76, figs. 51, 52), and 

 others by their base {figs. 53, 54). The earlier authors placed these animals 

 with the Mollusca, and the shells are often retained in conchological cabniets. 

 Their articulated cirrhi and double nervous axis indicate their true nature ; 

 and whilst they have been made a distinct class from the Crustacea, partly 

 on account of the supposed absence of an articulate structure, Dr. St. Ange 

 affirms that evident traces of such a structure exist. 



These animals undergo a metamorphosis, the young being bivalvular like 

 bivalve mollusca, and capable of swimming about freely for some time before 

 it affixes itself permanently. In this condition the limbs can be protruded 

 from the front of the shell ; the anterior pair being large, and provided with 

 a sucker and hooks for attachment to submarine bodies. The six posterior 

 pairs are used in swimming. The animal, at this period, bears considerable 

 resemblance to the small branchiopoda. Mr. Thompson, of Cork, placed 

 some of them in a vessel of sea water, and in a week's time two of them 

 had mantled and were affixed to the vessels as barnacles. A few days 

 afterwards, another individual was observed to throw off its shell and affix 

 itself. Both the orders of Cirrhopoda undergo these changes. 



The jaws are lateral, articulated, and toothed ; the cirrhi are articulated, 

 curved, and arranged along the abdomen, resembling somewhat the members 

 along the lower surface of the tail in the Crustacea. The class contains the 

 two orders Campylosomata and Acorn ptosomata., both of which are widely 

 distributed by floating wood, ships, sea-weed, mollusca, whales, turtles, &c. 



Order 1. Campylosomata. This order contains the pedunculated 

 flattened forms like Mitella (Oken, 1815; PolUcipes., Leach, 1S17, pi. 76, 

 fig. 51), and Lepas (Linn., 1748; Anatifa, Brug., 1792, pi. 76, fig. 52), in 

 which the shell is generally composed of two large lateral triangular basal 



iroxoGKAPHic encyclop^:dia. — VOL. II. 20 305 



