HELICINIDA. 227 
In 1824, Mr. Gray (Zool. Jowrn. p. 62) published a monograph 
of the genus, describing twenty-seven species; and in the same 
volume, p. 250, described two additional ones. He mentions the 
affinity of the genus to Cyclostoma, and pointed out the excellent 
character which the operculum affords for distinguishing it from 
that genus. He divided the species into five sections, which are 
now regarded as genera. 
In 1825, De Blainville (Man. Malac. 441), divided the genus 
Helicina into two sections: 1, Ampullina (H. striata) ; 2, Olygira 
(H. Neritella). 
In 1840, Mr. Gray (Syn. Brit. Mus. 134 and 153) formed the 
genus into a family, and considered three of the sections as 
’ genera, thus: “The shells of the Helicine have simple mouths; 
Alcadia differs in having a slit in front of the mouth, into which 
is fitted the tooth-like process of the operculum; and the Lucidelle 
are peculiar among operculated shells for having three or four 
teeth on the thickened edge of the mouth.” 
In the same year, Mr. Swainson (Malacology, ix. 337) divided 
the genus Helicina into four subgenera, by merely naming the sec- 
tions of Mr. Gray’s Monograph. § 1 is called Vrochatella; § 2, Oli- 
gyra; § 3, Helicina ; § 4, Pachystoma. He, like Ferussac, placed the 
toothed species, or sections 4 and 5 of Mr. Gray’s Monograph, 
in the family Helicide, under the name of Lweitdella, which 
Mr. Gray had already applied to the genus in the Museum 
Synopsis. 
Lister (Conch. t. 11, f. 59, t. 74, f. 72) and Patrick Browne 
(Hist. Jam. t. 40) first described and figured these shells. 
Mr. Gray, in the text of the figure of Molluscous Animals, calls 
the family Oligyradz, and refers to it the genera Oligyra, Alca- 
dia, and Steganostoma. 
To these genera must be added the recently-described genus of 
Stoastoma of Adams, which Mr. Gray described, under the name 
of Hlectrina, as a species of Cyclostomide, not having seen the 
operculum. 
I. STOASTOMA. 
Operculum not spiral, calcareous, externally very deeply concave, 
with lamellz slightly and irregularly projecting from the sur- 
face. Shell globose-conic, depressed or discoidal; aperture semi- 
oval or nearly semicircular, angulated above and beneath; 
peristome continuous, with the right margin arcuate, left 
margin nearly straight, sending off at its base a more or less 
distinct keel, which surrounds the more or less open perfora- 
tion. 
Stoastoma, Adams, Monograph of Stoastoma, 1849, p.3; Contrib. 
to Conch. n. 8, p. 148, n. 9, p. 158; Pfr. in Z. f. M. 1849, p. 113, 
