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 dubia. — Shell oblique, subovate convex, concentrically 
wrinkled, very 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 Tellina 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 writings 
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 Linnman system, in the latest 
edition of the Systema Naturae,” as before observed, consist of 
three orders. Multi vale. Bivalve, and Univalve, each of which is 
subdivided into genera. The Multivalves contain the Chiton, 
Leapas and Pholas ] the Bivalves, Mya, Solen, Tellina, Cardium, 
Mactra, Donax, Venus, Spondylus, Chama, Area, Ostrea, Anomia, 
Mytillus, and Pinna; and the Univalves, Argonauta, Nautilus, 
Conus, Cyprsea, Bulla, Yoluta, Buccinum, Strombus, Murex, Tro- 
chus. Helix, Nerita, Haliotis, Patella, Dentalium, Serpula, Teredo, 
and Sabella. Which see. See also Shells. 
[In the earlier editions of Mch. Enc. the following genera and species 
were not described : as the descriptions were only copied into the third 
