r>6 CLASSIFICATION. 



tion of the Rliipidoglossata (PectinibranchiMies) and Scutibran- 

 chiates, is the principal change. The arrangements of Gray and 

 Troschel ditfer still more, above all in the Androgyna, which are 

 placed between the Heteroglossa and Acephala, probably because 

 androgjaiisni is considered as a character of inferiority ; not- 

 withstanding that the Acephala, which are inferior, have the 

 sexes separate, with some exceptions. The little division, Pteno- 

 glossa, including only Janthina, Scalaria, Solarium, is placed, in 

 the system of Troschel, between the Khachiglossa and Rhipido- 

 glossa. If we admit a special concordance between the teeth of 

 these three groups, Morch still does not consider the difference 

 sufficient to justify a separation from the Androgyna. Janthina 

 appears to him more close to the Pteropods by its lateral wings, 

 and Scalaria, notwithstanding the position of the eyes, approaches 

 Chemnitzia. 



As in the entire animal kingdom, the greatest ditl'erence exists 

 amongst authors relative to the value of the swimming organs. 

 Tjatreille has united the Cephalopods and Pteropods in a single 

 division Pteiygia,to which he attributes the same value as to his 

 Apterygia, comprehending all other moUusks. Gegenbauer and 

 Huxle}' have demonstrated that the Pteropods are veritable 

 Gasteropods furnished with a pair of accessoiy swimming organs. 

 Already the discovery of Gasteropteron has shown the little value 

 of the Pteropods as a division equivalent to the Gasteropods. 

 The Heteropods merit still less to be considered as a division of 

 equal value. 



The late Prof. O. A. L. Morch, although attaching as much 

 systematic value to the lingual dentition as any other concholo- 

 gist, acknowledged that no single organ could be used in class!, 

 fication unless its differential characters accorded with differences 

 of other portions of the animal and shell ; but he endeavored to 

 show that conchologists have erred in estimating too highl}- for 

 systematic purposes the form of the shell, whilst neglecting 

 other external characters, such as sculpture, structure (nacreous, 

 porcellanous, etc.) and color. " According to ni}- views, one 

 must consider shells, so to say, from a mineralogical point of 

 view." Having thus chosen conehological characters heretofore 

 neglected, in grouping the genera and families, the discrepancies 



