132 LECTURES ON MOLLUSCA. 



authors take many things on trust, which humble students may prove 

 to be unfounded. It is a mistake to suppose that the evidence of the 

 senses is infallible. The eye has to be trained to see, just as much as 

 the ear to appreciate false and true harmonies,, or the hand to discrim- 

 inate weights. Very few persons at the beginning of their investiga- 

 tions see things in the microscope as they do after long study. The 

 best artist, if required to draw a shell, might very likely overlook 

 features which a student has learned to see at once. Therefore let a 

 man work some time, comparing his observations with the books, and 

 repeating them under different conditions, before he considers himself 

 competent to trust his own eyesight. 



Let the student especially avoid hasty conclusions. Because char- 

 acter A is found to be coordinate with character a in one class of 

 shells, let him not infer that it is so in another; still less that char- 

 acter B is coordinate with character b. The following table may 

 serve as a lesson of caution, to show how little can be gathered from 

 general similarity in appearance. It furnishes some of the more 

 striking examples of Gasteropods similar in form of shell, but known 

 to belong to different families by peculiarities in the animal. 



TABLE OF SIMILAR SHELLS, BELONGING TO DIFFERENT FAMILIES OR GENERA. 



Murex, Muricidce. Cerastoma and Vitularia, Purpuridce. Eanella 

 and Triton, Tritonidce. 



Chrysodomus, Muricidce. Strombella, Buccinidce. lo, Melaniadce. 



Engina, Muricidce. Ricinula, Purpuridce. 



Anachis, Muricidce. Nitidella, Purpuridce. Columbella, Buccinidce. 



Cominella, Muricidce. Buccinum, Buccinidce. Truncaria, ? Purpu- 

 ridce. 



Pisania, Muricidce. lopas, Purpuridce. Peristernia, Fasciolariadce. 



Pyrula, Pyrulidce. Fulgur, Fasciolariadce. Kapana, Purpuridce. 

 Ficula, Ficulidce. 



Leucozonia, Fasciolariadce. Monoceros, Purpuridce. 



Mitra, Fasciolariadce. Turricula, Turriculidce. Volutomitra, Volu- 

 tidce. 



Aulica, Volutidce. Amoria, Do. 



Metula, f Muricidce. Daphnella, Pleurotomidce. 



Marginella, Marginellidce. Erato. Cyprceidce. 



Cerithiopsis; Cerithiopsidce. Fastigiella, ? Fasciolariadce. Cerithium, 

 Cerithiadce. 



Velutina, Telutinidce. Capulus, Capulidce. Otina, Otinidce. 



Sigaretus, Naticidce. Lamellaria, Lamellariadce. Stomatella, Sto- 

 matidce. 



Drillia, Pleurotomidce. Clionella, Melaniadce. 



Lunatia, Naticidce. Lacuna, sp. Lacunidce. Pachistoma, Ampulla- 

 riadce. 



Naticina, Naticidce. Narica, Naricidce. Fossarus, Litorinidce. 



Menestho, Pyramidellidce. Mesalia, Turritellidce. Melania, Melani- 

 adce. 



Aclis, Pyramidellidce. Turritella, Turritellidce. 



Top-shells in general, e. g. : Solarium, Solariadce. Phorus, Phoridce. 

 Kisella, Litorinidce. Trochita, Calyptrceidce. Trochatella, Helici- 



