CONCHIFERS. 717 
As auditory organ, SIEPOLD regards a part met with by him in 
Cyclas, Anodonta, Unio, Mya, Cardium, Tellina, &c., an organ 
situated in front of and near to the nerve-mass of the foot. Here 
namely on both sides he found a vesicle in which a flat, round, 
transparent nucleus is in free motion. The nucleus is a concrement 
comparable to the Japilli in the auditory sac of the bony fishes}, 
Neither of this enigmatical organ nor of eyes has any vestige been 
met with in the Brachiopoda. 
The motions of these animals are very simple. Many Lamelli- 
branchiata, and all the Brachiopods, are fixed to their places, and 
are not able to move from them. Other conchifers have a springing 
motion by means of the foot, a name given to a production of the 
abdomen which is muscular and very firm, possesses great con- 
tractility and irritability, and may assume very different forms?. 
By means of it bivalves move at the bottom of the water in which 
they live. 
The geographic distribution of conchifers deserves a more 
special investigation than has hitherto been bestowed upon it. 
All conchifers live in water, part of them in fresh water, but 
the greatest part in the sea. Amongst the genera that live in 
the sea are some of which species are met with in all parts of 
the world, as genera Solen, Mya, Anatina, Mactra, Tellina, Lu- 
cina, Donax, Venus, Cardium, Arca, Pectunculus, Mytilus, Pecten, 
Ostrea. It is however far from the fact that all these genera 
are found in like manner in different seas; of the genera Venus, 
Cardium, Arca, Ostrea, the species are much more numerous in 
the Indian Sea and the South Pacific, than in seas of the northern 
hemisphere. Glycimeris appears to be a northern form, of which 
(ib. p. 153); they are particularly large and conspicuous in the species last named 
(Tab. 27, figs. 5, 14); Pour was not able to investigate their internal structure; and 
the later writers on the molluscs neglected this peculiarity altogether. Only within 
the last few years has it been adequately illustrated by GRruBE (MUELLER’s Archiv, 
1840, s. 24, Taf. 111. figs. 1, 3), KRroun (ib. s. 381— 386, Taf. x1. fig. 16) and Winn 
(Frorinp’s Neue Notizen, xxix, Bd. January, 1844, No. 622, 623). 
1 C. Tu. Von Sresoup Ueber ein rithselhaftiges Organ einiger Bivalven, MvELLER’s 
Archiv, 1838, s. 49—54 (transferred to Ann. des Sc. nat., sec. Série, x. Zool. Pp. 312), 
and WIEGMANN’S Archiv, 1841, Ueb. d. Gehirorgan der Mollusken, s. 148 and foll., 
Ann. d. Sec. nat., sec. Série, XIX. p. 193, Pl. 2B, fig. 1. [Also Leypie Ueber Cyclas 
cornea, MUELLER’S Archiv, 1855, pp. 51, 52. Pl. vi. fig. 18.] 
* See Pout, 1. Jntrod. p. 37. 
