388 Dr. 0. A. L. Morch on the Systematic Value of the 



and Greenland. A. pes-pelecani and a variety, perhaps specifi- 

 cally distinct, are found from the north of Norway to the Medi- 

 terranean. In Shetland a second species is added, the A. pes- 

 carbonis, which in the Mediterranean is represented by A. Ser- 

 resiana, Phil. In Senegal is found A. senegalensis, Gray. The 

 most northern species is the largest of the genus, as is generally 

 the case ; the outside of the outer lip is smooth, as in all other 

 arctic univalves. In A. pes-pelecani and the following southern 

 species the inside lip is plaited, as is generally the case in species 

 of warmer climes (e. g. Nassa and other univalves). The A. 

 senegalensis, living in the hottest water, is the smallest. Un- 

 fortunately it will be very difficult to get the tongues of these 

 species. The teeth of Aporrhais pes-pelecani as represented by 

 Loven, Troschel, and Wilton differ considerably from one an- 

 other, making it probable that two species are confounded. 



A monographic research, chiefly based on the teeth of the 

 genera Nassa, Fusus, and Buccinum, found on the coast-lines 

 from the arctic regions to the equator, would probably be suffi- 

 cient to prove whether species in each fauna are created originally 

 or are only varieties dependent on diiferent climates, and would 

 at the same time prove the relations between the species of suc- 

 ceeding geological periods. 



Lai'ge suites of specimens, from various depths and localities, 

 are in most cases sufficient to prove the difference or identity of 

 so-called species, without a knowledge of the animals ; but the 

 affinity of the genera and families can only be safely understood 

 by anatomical researches : the anatomical as well as the zoolo- 

 gical characters are, however, generally either misunderstood or 

 overvalued. I will therefore endeavour to show the relative 

 systematic value of the various organs of the Mollusca. Until 

 these questions are quite cleared up, it will not be possible to 

 solve the problem in regard to the origin of species among the 

 Mollusca, 



Cuvier founded his primary divisions (classes) of the Mollusca 

 on the locomotive organs, viz. Cephalopoda, Pteropoda, Gastero- 

 poda, Acephala (this last changed by Oken to Pelecypoda), 

 Brachiopoda, and Cirrhopoda. The group Heteropoda, correctly 

 considered by Cuvier only a family, was by most subsequent 

 naturalists considered of the same value as the above-mentioned 

 divisions. The study of the homology of the parts of the Mol- 

 lusca, commenced by Professors Loven and Huxley, has shown 

 that the Pteropoda are true Gasteropoda, and that the funnel of 

 the Cephalopoda is homologous with the foot of theGymnosomata. 

 Such a system seems to me to correspond with that classification, 

 by the old authors, of the Vertebrata (Quadrupeda, Bipeda, 

 Pinnata, and Apoda), maintained so pertinaciously by Klein in 



