307 



CLASS V. BRACHIOPODA. 



Body covered by a two-lobed, open mantle, and en- 

 closed in a bivalve shell ; head not distinct ; mouth with 

 two fleshy, extensile arms or filaments ; no foot. 



Brachidpoda, Cuvier. Bpaxuov, an arm ; TTOVS, a foot. 



No species of this comparatively small class has 

 occurred to me, although it is probable that some exist 

 in the district. 



CLASS VI. APODA. 



Body enclosed in a dense sac, having two small aper- 

 tures ; head not distinct ; mouth and anus connected 

 with the external apertures ; branchiae diversiform, but 

 not divided into four laminae, and always contained in 

 the interior of the body. 



Ascidia, Linnaeus. Acephala in-test dcea, Cuvier. 

 Heterobranchidta, Blainville. 'A, without ; TTO&X, feet. 



The sixth class of the Malacozoa is composed of ani- 

 mals presenting considerable affinity to those of the class 

 of Tropiopoda, but differing so much from them as to 

 merit a separate section for themselves, and even in such 

 a degree as, in the estimation of many naturalists, to 

 render their position doubtful. They are destitute of a 

 head and special organs of sense, and are placed in an in- 

 verted position, or with the mouth below, and the anal 



