234 Description of the Plates. 



been removed. The shell having been removed^ the hinge 



process is figured as broken. 

 c. Laminated portions of oviducts, opening by an expanded orifice 



into the perivisceral cavity. In Rhynchonella there are four 



oviducts, one pair within the ventral, the other within the 



dorsal valve. The dorsal oviducts open into the perivisceral 



cavity by orifices looking forwards and upwards ; the ventral 



by orifices looking backwards. 

 c. Tubular portions of oviducts, opening downwards. Those of 



the dorsal oviducts open above the mouth, those of the 



ventral below, into the mantle cavity. 

 p. Peduncle passing through a foramen, which is incomplete in 



young shells, to be attached by a pair of muscles within the 



umbo of the ventral valve. 

 m. Ocelusor muscle. 

 m 2. Divaricator muscle, passing from ventral valve to cardinal 



process of dorsal. 

 m ^. Adjuster muscle, passing from hinge process in the dorsal 



valve into the peduncle. 

 m 4. Adjustor muscle, passing from ventral valve into peduncle. 

 ms. Mesenterial lamina, connecting the two limbs of the bent 



tube made up by the digestive tract, and supporting the 



expanded inner segments of each of the four oviducts. 



For a figure giving more details of the anatomy of Bliynclionella 



Psittacea, see Hancock, Phil. Trans., 1 858, pi. Ixi., fig. 2. 

 For figures of the nerve system, see Hancock, ibid., p. 845, pi. Ixii. 

 For the various names which have been applied to each of the two 



valves, see Lacaze Duthiers, Ann. des Sciences Naturelles, 



Ser. iv., tom. xv., i86r, p. 266. 

 For the various views which may be taken as to the relationship of 



the class, see Lacaze Duthiers, Comptes Rendus, 1865, ii., 



p. 800; Hancock, I. c, p. 848. 

 For the entire organization of the Brachiopoda, see Hancock, /. c, 



ibique citata, and Lacaze Duthiers, U. citt. 

 For a description of a larval form of Brachiopod, see Fritz Miiller, 



in Reichert and Du Bois Reymond's Archiv., t86o, p. 72; 



Me Crady, Silliman^s Journal, i860, xxx., p. 157. 



