346 MOLLUSCA SUB-KINGDOM VI 
Class I. PELECYPODA. Goldfuss.1 
(Lamellibranchiata, Blainville ; Conchifera, Lamarck ; Bivalvia (Bonanni), Linne ; 
Lipocephala, Lankester.) 
Aquatic, bilaterally symmetrical, acephalous mollusks, protected by a pair of 
shelly valves, which are secreted by the lateral portions of the mantle, connected by 
a ligament, and moved. by the contraction of muscles attached to the inner faces of 
the valves ; feeding by ciliary action and destitute of a radula or jaw ; breathing by 
lateral gills ; imperfectly sensible to light and rarely provided with peripheral visual 
organs ; possessing olfactory organs (osphradia), auditory and equilibrating organs 
(otocysts), tactile papillae, and a nervous system composed of ganglia united by 
nerves, but without a pedovisceral commissure ; provided with an extensile, tactile, or 
locomotor organ (foot); a circulatory system containing haemolymph, and operated 
by a single or paired cardial ventricle and two auricles ; a more or less convoluted 
intestinal canal, with its oral and anal extremities at opposite ends of the body; a 
stomach ; paired nephridia, connected with the pericardium, and discharging in- 
dependently of the rectum ; reproducing without copulation, by eggs and spermatozoa ; 
monoecious or dioecious ; development external to the ovary, the post-larval stage 
protected by a prodissoconch, and sometimes exhibiting a special nepionic stage. 
External Characters. The Shell—The embryonic Pelecypod is pro- 
vided with a saddle-shaped, single shell gland, which secretes a pellicle of the 
same form, upon which, at two points corresponding to the valves, calcification 
sets in independently. These rudiments remain connected across the dorsum 
1 Literature (see also, under the head of Mollusca, pp. 344-345) : 
Wood, S., Monograph of the Eocene Bivalves of England (Palaeont. Soc.), 1861. 
Zittel, K. A. von, Die Bivalven der Gosaugebilde (Denkschr. der Wiener Akad., XXV.), 1865-66. 
Coquand, H., Monographie du genre Ostrea des terrains cretacés, 1869. 
Barrande, J., Systeme Silurien de la Bohéme (Acephales, vols. I.-IV.), 1882. 
Béhm, G., Die Bivalven der Stramberger Schichten (Palaeont. Mittheil. Mus. Bay. Staates, II.), 1883. 
Neumayr, M., Zur Morphologie des Bivalvenschlosses (Sitzungsber. Wiener Akad. Bd. LX XXIII), 
1883.—Ueber die Herkunft der Unioniden (id., Bd. XCVIII.), 1889. 
White, C. A., Review of the fossil Ostreidae of North America (Ann. Report U.S. Geol. Survey, for 
1883), 1884. 
Hall, J., Geological Survey of New York, Palaeontology, vol. V., 1884-85. 
de Koninck, L. G., Fauna du Caleaire carbonifére de la Belgique (Ann. du Mus. d’hist. nat. de 
Belgique, vol. V., pt. 5), 1886. 
Dall, W. H., On the Hinge of the Pelecypods and its development, ete. (Am. Journ. Sci. [3], vol. 
XXXVIII.), 1889. 
Jackson, R. T., Phylogeny of the Pelecypoda. The Aviculidae and their Allies (Mem. Boston. Soe. 
Nat. Hist., vol. IV., No. 8), 1890. 
Menegaux, A., Recherches sur la circulation des Lamellibranches marines, 1890. 
Neumayr, M., Beitriige zu einer morphologischen Eintheilung der Bivalven ; mit Vorwort von E. 
Suess. (Denkschr. Wiener Akad., Bd. LVIII.), 1891. 
Hyatt, A., Remarks on the Pinnidae (Proc. Boston Soc. Nat. Hist., XXV.), 1892. 
Moynier de Villepoix, R., Recherches sur la formation et l’accroissement de la Coquille des 
Mollusques. Thesis, 1893. _ 
Ulrich, E. O., New and little known Lamellibranchiata from the Lower Silurian Rocks of Ohio, ete. 
(Rept. Geol. Surv.” Ohio, vol. VII.), 1893.—New and little known Lamellibranchiata of 
Minnesota (Rept. Geol. Surv. Minn., vol. III.), 1894. i 
Bernard, F’., Premicre note sur le developpement et la morphologie de la coquille chez les Lamelli- 
branches (Bull. Soc. Geol. de France [3], vol. XXIII.), 1895. ; 
Dall, W. H., A new Classification of the Pelecypoda (Trans. Wagner Inst. Sci. Philadelphia, vol. 
III., pt. 3), 1895. Also Proc. U.S. Nat. Mus., vol. XVII., No. 1032, 1895. 
Hyatt, A., Terminology proposed for the Description of the Shell in Peleeypoda (Proc. Am. Assoc. 
Adv. Sci. vol. XLIV.), 1895. 
