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. Linnaeus first 

 based the system of M amnialia, 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 maxillae of the 

 Arthropoda. The maxilla is a median, unequal-sized, corneous 

 plate attached to the bulbus pharyngeus over the oral aperture, 

 and serving to divide the food into morsels. It is found in all 

 Land Pulmonata (Phyllovora, Gray). According to its struc- 

 ture, I have distinguished the following groups: — Oxygnatha, 

 with a smooth maxilla; Aulacognatha, with a closely sulcated 

 maxilla, crenulated at the edge ; Oaontognatha, with a strongly 

 ribbed maxilla, forming projecting teeth on the edge; Gonio- 

 gnatha, with the maxilla composed of oblique plates (genus 

 Orthalicus)-f. 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, Urucoptis, Glandina). Among 

 the marine Mollusca, it is only found in jEgirus and, perhaps, 

 Sip hono dent alium. 



* Ofversigt af Kgl. Vetenskaps Akademiens Forhamllingar, 1847. 

 t Morch, Malacozoologische Blatter, 1859. 



Ann. $ Mag. N. Hist. Ser. 3. Vol.xvi. 6 



