GASTEROPODA PECTINIBRANCHIATA. 359 



completed, also, by the penultimate whorl; but the shell is thin, and 

 is so far from being convoluted in one plane, that its spire is pro- 

 longed into a turreted obelisk. The eyes of the animal are placed 

 on the external base of its tentacula; the foot is small(l). 



They are found in great numbers among fossils; the Proto, 

 Defr., should be approximated to them. 



ScALARiA, Lam. 



The spire, as in Turritella, elongated into a point, and the aper- 

 ture, as in Delphinula, completely formed by the last whorl; it is 

 moreover surrounded by a ridge, which is formed from space to 

 space as the shell of the animal increases in size, resembling so 

 many steps. The tentacula and penis of the animal are long and 

 slender. 



One species celebrated for the high price it commands(2), 

 the Turbo scalaris, L.; Chemn., IV, clii, 1426, Sec. vulg. Sca- 

 lata, is distinguished by the Avhorls only coming in contact at 

 the points where the ribs unite them, the intervals being open. 

 A second species, the Turbo clathrus, L. ; List., 588, 50, 51, 

 is not marked by this peculiarity; it is more slender, and very 

 common in the Mediterranean. 



Some terrestrial or fresh water subgenera, in which the 

 aperture is entire^ round, or nearly so, and operculated, may 

 be placed here. Of this number is the 



Cyclostoma, Lam. (3) 



The Cyclostomse should be distinguished from all the others be- 

 cause they are terrestrial, as instead of branchiae, the animal has 

 merely a vascular network spread over the parietes of its pectoral 

 cavity. In every other respect, however, it resembles the other 

 animals of this family; the respiratory aperture is formed in the 



(1) Turbo imhrlcatus. Martini, IV, clii, 1422; — T. replicatus, lb., cli, 1412; List., 

 590, 55; — T. acutangulus. List., 591, 59; — T. dupUcatus, Martini, lY, cli, 1414; — 

 T. exoletus, List., 591, 58;— T. terebra, Id., 590, 54;— 71 varicgatus, ^Martini, IV, 

 clii, 1423;— T: obsoktus. Born., XIII, 7. 



(2) Enormous sums have been paid for this shell, which is the Wentletrap of 

 collectors and dealers. One in Bullock's jMuseum, London, was valued at two 

 hundred guineas, and four specimens, at one sale, brought from sixteen to twenty 

 odd pounds sterling- eacli. The price now is reduced, but a decent specimen is 

 still worth several guineas. Am. Ed. 



(3) The Cyclosiomse and the Helicines form the order of the Pdlmoxea Opercc- 

 LATA of M. de Ferussac. 



