LECTURES ON MOLLUSCA. 133 



Especially: Phorus, Phoridce, Guildfordia. Turbidce. Torinia, So- 

 lariadce. Monilea, Trochidce. Infundibulum, Trochidce. Trochita, 

 Calyptrceidce. 



Rostellaria, Strombidce. Aporrhais, Aporrhaidce. 



Tanalia, Paludinidce. Paludomus, Melaniadce. 



Yermetus, Vermetidce. Serpula, ANNELIDS. 



Dentalium, Dentaliadce. Ditrupa, ANNELIDS. 



Planorbie, Planorbidce. Marisa, Ampullariadce. Polygira. Helicidce. 



Limpets in general, e. g. : Patella, Patellidce. Acmasa, Acmceidce. 

 Amalthea, Capulidce. Gadinia, Gadiniadce. Siphonaria, Siplionari- 

 adce. Broderipia, Stomatidce. Umbrella, Umbrellidce. 



Especially : Nacella, Patellidce. Ancylus, Planorbidce. Latia, Pla- 

 norbidce. Oepidula, CatyptrceidcB. Tylodina, Umbrellidice. Scurria, 

 Arm&idce, 



Amphibola, Ampliibolidce. Scissurella, Scissurellidce. 



Achatina, Helicidce. Glandina, Testacellidce, &c. &c. 



A similar table might easily be prepared of shells very greatly dif- 

 fering in appearance, which are known to belong to the same family. 



This branch of study has been favored with quite a sufficient num- 

 ber of hasty generalizations to last for some time to come. What we 

 want now is patient verification of the past, and cautious observation 

 for the future. "Non omnes possumus omnia," and every man is not 

 bound to do his work well ; because he cannot ; but he is bound hon- 

 estly to use all the materials at his command. There is so much yet 

 to be known about the commonest land and fresh-water shells, in their 

 anatomy, habits, distribution, and specific differences ; and there are 

 so many materials hoarded up in museums awaiting the study of nat- 

 uralists, that all who are disposed to train their eyes and set to work 

 can easily find the means for useful service. 



The objects of the Smithsonian Institution are both the increase and 

 ihediffusion of knowledge. So very much confusion is constantly arising 

 from wrongly or uncertainly named specimens, that those who are not 

 prepared to increase existing knowledge can make themselves very 

 useful simply by diffusing the knowledge of others. On comparing 

 together the American shells given me by a number of accurate and 

 trustworthy American naturalists, I find myself considerably bewil- 

 dered, not merely by the wrong names which are given, but by names 

 given as by Lea, Say, and other distinguished authors, which contra- 

 dict themselves, and therefore cannot be depended upon. These diffi- 

 culties are to be met by the copious diffusion of specimens named from 

 types. All that can thus be vouched for have a peculiar value, espe- 

 cially in a foreign country : and if collectors will merely amass a 

 multitude of specimens, and see to their being named by those who 

 possess the typical knowledge, the Smithsonian Institution will see to 

 their being made available for the purposes of science. It is not neces- 

 sary for the uses of science that the name given should ultimately stand 

 as the correct one. Whether, e. g., among the Unios, a name of Lea 

 or of Eafinesque be permanently chosen, matters little. What we 



want to know is that such a shell is really the Unio of Lea, or the 



Unio of Conrad. When it is known accurately what each author 



means by his own descriptions, his successors have something tangi- 



