274 MOLLUSCA. 



flat and fixed to a rock. The arms of the animal, Criopus, Poll are ciliated 

 and spirally recurved like that of the Lingulse. 



CRANIA, Brugui&res, 



Should be approximated to the Orbicula?. The arms of the animal are also 

 ciliated, but the shells have deep and round internal muscular impressions, 

 that have caused it to be compared to the figure of a skull. 



One of them inhabits European seas; Anomia craniolaris, Lin. Several 

 are fossil ; such as the Cran. antiqua, and the others of which M. Hoening- 

 haus has given an excellent monograph. 



CLASS VI. 

 CIRRHOPODA. 



LEPAS AND TRITON, Linn&us. 



THE Cirrhopoda, in several points of view, are intermediate between 

 this division and that of the Articulata. Enveloped by a 

 mantle, and testaceous pieces which frequently resemble 

 those seen in several of the Acephala, their mouths 

 are furnished with lateral jaws, and the abdomen with 

 filaments named cirri, arranged in pairs, composed of a 

 multitude of little ciliated articulations, and corresponding 

 to a sort of feet or fins similar to those observed under the 

 tail of several of the Crustacea. Their heart is situated 

 in the dorsal region, and the branchite on the sides ; the 

 Anatifa. nervous system forms a series of ganglions on the abdomen. 

 These cirri, however, may be considered as analogous to the arti- 

 culated appendages of certain species of Teredo, while the ganglions in 

 some respects are mere repetitions of the posterior ganglion of the 

 bivalves. The position of these animals in the shell is such, that the 

 mouth is at the bottom and the cirri near the orifice. These animals 

 are always fixed. Linnaeus comprised them all in one genus, LEPAS, 

 which Brugieres divided into two, that have in their turn been sub- 

 divided. 



ANATIFA, Bruguicres. 



A compressed mantle, open on one side and suspended to a fleshy tube, 

 varying greatly as to the number of testaceous pieces with which it is 

 furnished ; twelve pair of cirri, six on each side, those nearest to the mouth 

 being the thickest and shortest. The branchia? are elongated pyramidal append- 



