2 CATALOGUE OF PHANEROPNEUMONA. 
The Mollusca of this order show a structure which is very 
similar in the whole group, and by which they may be easily dis- 
tinguished from the other terrestrian Mollusca (Limacide, Heli- 
cid, Auriculide). They are divided into two sexes (never her- 
maphrodite, as Helicide), and provided with two contractile 
tentacles, with the eyes on the posterior or outer side of their 
base. The mantle has sometimes a free edge, sometimes it is 
affixed and concealed in the shell, a character by which Ferussac 
has distinguished his families of Helicine and Turbicina. 
This order of Mollusca was first proposed by Dr. Gray, in his 
Essay on the Arrangement of Mollusca (Medical Repository, 
1821), as the second order of the Pneumobranchiata to include 
the genera Cyclostoma and Helicina. M. Ferussac, in the same 
year, 1821 (Zadl. Syst. p. xxxili.), established it as the fifth 
order of Gasteropoda, under the name of Pulmonata operculata; 
and proposed to unite the two genera, Helicina and Cyclostoma, 
the very close natural affinity of which had been overlooked by 
all preceding writers, not excepting Cuvier and Lamarck. Each 
of these genera constitutes the type of a distinct family, Helicinze 
and Turbicina. 
Latreille, 1825 (Fam. Nat.), has imposed the name of Pnewmo- 
poma to the first order of dizecious Gasteropoda, which he divided, 
like Ferussac, into the families of Helicinide and Turbicina. 
The same order was designated, 1828, by Menke (Syn. p. 22) 
with the name of Celopnewmonata operculata. He considers it 
as the sixth order of Gasteropoda, and divides it into the families 
Helicinacez and Cyclostomiate. In the second edition (1830, 
p- 39) he changes the name of the order into Coelopnoa operculata, 
and that of the families into Helicinacea and Cyclostomacea. 
Deshayes (1830, Eneyel. Meth. iii. p. 552, Tabl.) proposed the 
name felicinea for the third family of Pulmobranchiata, com- 
prising the generas Cyclostoma, Strophostoma, and Helicina. 
Wiegmann (1832, Handb. d. Zool. p. 527) has designated the 
same order with the name of Pulmonata operculata. Its genera 
are Cyclostoma, Helicina, Steganotoma, and Pupina. 
Anton (1839, Verzeichn. p. xiii. 52) designates with the name 
of Cyclostomacea, a family, comprising Cyclostoma, Helicina, 
and Littorina. 
Hartmann (1840, Zrd wu. Sussw. Gast. Syst. Uebers.) unites under 
the name of Pseudobranchiata, or Teleogeophila, the EKuropean 
genera, Choristoma, Pomatias, and Cyclostoma, omitting Helicina 
as a tropical genus. 
The Prnewmonobranchiata operculata of Gray (1840, Turt. Man. 
ed. alt. p. 273) is intended to include the Helicinide. 
D’Orbigny (1841, Moll. Cuba, i. p. 199, 236) admits in the first 
family of dizecious Pectinibranchiata the division Cyclostomide, 
comprising the genera Odontostoma, Helicina, Cyclostoma, and 
Strophostoma. 
