302 PTEEOPODID^E. 



small part of the year proves nothing as regards the plan of 

 respiration, as the Rissoa ulvce and minute Littorince 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 branchiae ac- 

 quire the capability of extracting oxygen therefrom. Though 

 the C. bidentatus are so little submerged, the places they lie 

 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 frilly as in C. denti- 

 culatus, that this animal in like manner breathes free air. 



PTEEOPODID.E. 



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. 



