THE ANNALS AND MAGAZINE OF NATURAL HISTORY. [THIRD SERIES.] No. 92. AUGUST 1865. VIII. — On the Homology of the Buccal Parts of the Mollusca. By Dr. Otto A. L. Morch, of Copenhagen. [Plate VI.] The oral organs have, throughout the animal kingdom, furnished some of the most important systematic characters. Linnseus first based the system of MammaUa, and Fabricius that of Insects, upon the structure of these parts. It was, however, not until 1847 that Prof. Loven* placed the natural classification of the Mollusca on a scientific base, chiefly founding it on the dentition of the tongue (radula). Another part of the oral organs, the mandibles, has been much neglected. Most authors understand by this name all hard bodies near the entrance of the mouth. I believe it is necessary to distinguish two (or perhaps three) different kinds of oral plates corresponding to the mandibles and maxillce of the Arthropoda. The maxilla is a median, unequal-sized, corneous plate attached to the bulb us pharyngeus over the oral aperture, and serving to divide the food into morsels. It is found in all Land Pulmonata (Phyllovoi'a, Gray). According to its struc-ture, I have distinguished the following gi-oups : — Oxygnatha, with a smooth maxilla; Aulacognatha, with a closely sulcated maxilla, crenulated at the edge ; Odontognatha, with a strongly ribbed maxilla, forming projecting teeth on the edge; Gonio-gnatha, with the maxilla composed of oblique plates (genus Orthalicus)-^. Among the Land Pulmonata, the maxillae are wanting in the Agnatha (Vermivora, Gray), which swallow their prey entire and alive (genera Onchis, Testacella, Helicophanta, Caffra, Daudebardia, Streptaxis, Urocoptis, Glandina). Among the marine Mollusca, it is only found in jEgirus and, perhaps, Siphonodentalium. * Ofversigt af Kgl. Veteaskaps Akademiens Forhandlingar, 1847. t Morch, Malacozoologische Blatter, 1859. Ann. ^ Mag. N. Hist, Ser.3. Vol.xvi. 6
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