302 PTEROPODIDA. 
small part of the year proves nothing as regards the plan of 
respiration, as the Rissoa ulve and minute Littorine adhere 
constantly to the outside of the bases of the stones under 
which the Conovuli are found, and are not more submerged, 
and yet these animals are decided Pectinibranchiata, which 
nevertheless appear to have the power of living in free air 
with almost equal facility as the Pulmonifera, and perhaps, 
by constant exposure to the atmosphere, their branchiz ac- 
quire the capability of extracting oxygen therefrom. Though 
the C. bidentatus are so little submerged, the places they he 
in are always humid from the influences of the tidal waters. 
Before the Conovulus denticulatus had been met with, we 
had placed this animal in that genus, but the foot of the 
former being, by its integrity, so very different from the trans- 
versely divided foot of this species, together with the curious 
locomotion, have induced us to substitute Adanson’s Pedipes 
for Conovulus. Since the above was written, the occurrence 
of very large specimens has assured us, as fully as in C. denti- 
culatus, that this animal in like manner breathes free air. 
PTEROPODID . 
This family embraces the Pteropoda of Cuvier and Lamarck. 
We refer to the analysis of our classification for the reasons 
why this division is reduced in our method to a simple family 
of hermaphrodite animals with congression, of the Cryptibran- 
chiata; which branchial division receives those animals that 
have the respiratory apparatus deposited in distinct furrows 
or crypts in various parts of the dorsal region, and in that 
respect differ, though not very essentially, from the Cervico- 
branchiata. Hyalea and Spirialis are the only British genera ; 
but the species, of which only unique specimens have occurred, 
are so obscure as almost to baffle description. The Spirialis 
Flemingii is the exception, which is not uncommon ; but the 
recorded accounts of all the animals are so scanty and unsatis- 
factory as to afford little information. 
