290 AMERICAN JOURNAL 



disjointed, it is very close to the other centres. Again, in the 

 Helices, the Testacellge, the Limaces, etc., its five ganglia lie 

 upon the pedal centre, and are united to it in such a manner by 

 a common conjunction tissue, that they have been described as 

 the posterior pedal ganglia. 



In the Aplysifie, the Bullese, all the Pectinibranchia, and the 

 Cyclostomata, the commissure which unites the inferior ganglia 

 is long and twisted, and the homologous parts are difficult to rec- 

 ognize. Notwithstanding this, the general connections remain 

 constantly fixed. 



With regard to the mantle, the following facts leave no doubt. 

 By numerous dissections of the most different types, I believe 

 I am able to establish that this part of the body is exclusively 

 innervated by the inferior centre, and that henceforward we may 

 define it thus : — Any fold or cutaneous part of the body of the 

 Gasteropod receiving nerves from the inferior or unsymmetrical 

 centre, is either the mantle or a dependence of the mantle. The 

 forms of the pallial fold may vary infinitely, their connections 

 never. How, therefore, can we, in Aplysi?e, regard the two 

 large lobes which ascend at the back and at each side expose its 

 back as being dependencies of the mantle, when their nerves all 

 come from the pedal ganglia ? These lobes are the foot itself, 

 and serve for swimming. 



The dorsal shield of the Limaces is the mantle very slightly 

 developed ; it receives all its nerves from the inferior centre ; 

 and the part which is drawn out along the lower part of the body 

 and contains the viscera, is the foot, for its nerves are derived 

 from the anterior centre. Again, in the Testacellge, it is the 

 upper part of the neck and of the foot which becomes developed 

 and lodges the organs. The connections of the nerves show the 

 mantle reduced to that inferior part which covers the shell. 



These examples suffice to prove the utility of the principle, 

 which will lead us to a single scheme, the true theoretical and 

 the ideal archetype of the Gasteropod. — Comptes Rendiis, De- 

 cember, 27, 1869, tome Ixix, p. 1344. 



A new British Land Shell. By J. Gwyn Jeffreys. 



Helix glahi^a, Studer, a continental species, is now first re- 

 corded as British. 



Observations on the Geology and Zoology of Abyssinia. By W. T. 



Blanford. 8yo. Loudon, 1870. 



Contains : 1. A list of Oceanic Mollusca obtained off the S. E. 

 coast of Arabia. 2. Marine Mollusca from Annesley Bay. 3. 



