PULLUSTEA. 255 



recent species are enumerated in Pt. 2. of the Author's 

 Thesaurus Conehyliorum. PL ii. P. aurantiaca. PL xviii. 

 fig. 405. 



PTEROCYCLOS. Benson. Syn. B. M. p. 133. A genus formed 

 of species of Cyclostoma, Auct. which have " a groove or hole at 

 the hinder part of the mouth." Ex. Cy. bilabiatum. Thesaurus 

 Conehyliorum, PL xxv. fig. 82. 



PTEEiOPODA. Lam. (Trrepov, pteron, a wing ; ttovq, pous, a foot.) 

 The first order of the class Mollusca, Lam. consisting of molluscs 

 whose organs of locomotion consist of a pair of wing-shaped fins. 

 This order contains the genera Hyalsea, Clio, Cleodora, Spiratella, 

 Cymbulia, and Pneumoderma. To which may be added other 

 genera enumerated in explanation of figures 220 to 226. They 

 may be thus distinguished. 



1. Atlanta. Shaped like Nautilus, symmetrical. Pig, 220. 



2. Spieatella. Spiral, not symmetrical. Fig. 224. 



3. Ceeseis. Straight, thorn-shaped. Pig. 222. 



4. Vagintjla. Straight, widened in the centre ; apex pointed. 



Pig. 225. 



5. CuYiEEiA. The same ; apex blunt. Pig. 223. 



6. Cleodoea, Aperture with three spines ; apex recurved. 



Pig. 221. 



7. Htaij^a. Vaulted, open extremity, three-cornered ; apex 



tridentate. Pig. 226. 



PTEEOPODA. BL The second famHy of IS'ucleobranchiata, 

 Bl. the shells of which are described as symmetrical, extremely 

 thin, transparent, longitudinally enrolled, either forwards or 

 backwards. The animals are remarkable for a pair of broad, 

 flat, swimming paddles or membranaceous fins, from which the 

 family derives its name. It contains, in the system of De 

 Blainville, the genera Atlanta, Spiratella, and Argonauta, to 

 which may probably be added Phaeeteitjm, Konig ; Entaiis, 

 Defranee. 



PULLUSTEA. Sow, Tapes, Megeree. Fam. Oonques Marines, 

 Lam. — Bescr. Equivalve, ovate or oblong, transverse, inequi- 

 lateral ; hinge with three diverging cardinal teeth in each v^ve, 



