55 



men three pale yellow active young ones were taken, the largest 

 of which measured in breadth three-twentieths of an inch in the 

 month of May. 



Cylas DuniA. — Shell oblique, subovate convex, concentrically 

 wrinkled, veiy pale horn color or whitish, with sometimes a darker, 

 but not raised band, marking the preceding year's growth of the 

 shell ; beaks placed much nearer one end ; within whitish, primary 

 teeth very distinct, in one valve two divaricating ones, in the other 

 but one; exterior laminal tooth very small. Length, five-twentieths 

 of an inch ; breadth, three-tenths. Plate 1, fig. 10. 



Inhabits the river Delaware in company with C. similis, and very 

 much resembles TelUna amnica of authors. 



The shells here described are in the collection of the Academy 

 of Natural Sciences of Philadelphia. 



It was originally the intention of the writer of this article to 

 insert here, not only descriptions of the fresh water and land shells, 

 but those of the coast also ; finding, however, that the descriptions 

 of the latter were by far too voluminous to be comprised within the 

 space allotted to this article, and that they had more generally 

 found a place in the systems, the design is, with respect to this 

 work, necessarily relinquished. To all the species here described, 

 with the exception of three or four, we have been constrained to 

 adapt specific names ; but should it appear that we have been anti- 

 cipated by the labors of some recent conchologist, whose wi'itings 

 we have no opportunity to consult, we shall readily bow to the 

 right of priority, which ought unquestionably to be on all occasions 

 imperative and exclusive. 



The primary divisions of the Linnjean system, in the latest 

 edition of the " Systema Naturae," as before observed, consist of 

 three orders, Multivale, Bivalve, and Univalve, each of which is 

 subdivided into genera. The Multivalves contain the Chiton, 

 Leapas and Pholas ; the Bivalves, Mya, Solon, Tellina, Cardium, 

 Mactra, Donax, Venus, Spondylus, Chama, Area, Ostrea, Anomia, 

 Mytillus, and Pinna ; and the 'Univalves, Argonauta, Nautilus, 

 Conus, Cypraea, Bulla, Voluta, Buccinum, Strombus, Murex, Tro- 

 chus. Helix, Nerita, Haliotis, Patella, Dentalium, Serpula, Teredo, 

 and Sabella. Which see. See also Shells. 



[In the earlier editions of Nich. Enc. the following genera and species 

 were not described : as the descriptions were only copied into the third 



