320 CRETACEOUS GASTROPODA 
II. Swub-order,—Cervicobranchiata. 
[Char. Gill single on the left side of the gill-cavity on the back of neck; teeth in a few 
longitudinal series, forming arched ecross-series of two or three pairs. Shell conical, cup-shaped, 
symmetrical, with the apex subspiral or simply pointed. (Vide Gray, Guide, 1857, p. 169). 
This sub-order is here introduced simply for the sake of convenience of a sub-division, as 
it includes all the Patel/i—form shells, the animals of which only differ from those of the 
CyctoprancnHtatTa by their gills being single. Gray includes in it three families, the LEZPETIDA, 
TecTurIDZ and GADINIDZ. To these the SrpHONARIIDa may be added, as they agree in most 
of the important characters especially with the last named family]. 
XLIV. Family,—TECTURIDZ. 
H. and A. Adams, Genera I, p. 458; Gray, Guide, 1857, p. 169; Scurz~zm#, Chenu, 
Man. I, p. 3874. 
The animals of the Tzcrvrrp# in general very much resemble those of the 
Pararirm.s, except that they have the mantle margin not, or only slightly, fringed ; 
the head has a short muzzle, mouth with cartilagimous jaws, tentacles subulate, 
short, eyes on bulgings at the outer and upper bases of the former; teeth in six 
longitudinal series, the two inner close, uniform and often larger than the two 
outer ones on each side; foot large, thick and ovate, usually with an impressed 
groove in the middle ; no operculum. 
The shells are depressed, conical, with large open mouth and a subcentral or 
excentric, more or less pointed and incurved, apex ; the muscular impression is inter- 
rupted in the region of the gills near the head. 
The species are mostly littoral, feeding on seaweeds, or on different marine algze 
on the rocks. They are often found, with Patelle, between the tide marks 
attached to the rocks; being as a rule truly marine inhabitants and numerously re- 
presented among living shells. W. Blanford lately described (Jour. As. Soc., 1867, 
pt. II, p. 62, pl. 18, figs. 2-4) a Tectwra fluviatilis from the brackish water at the 
mouth of the Irravadi river, where it usually lives attached to the rocks. The shell 
is broadly conical, remarkably thin, with very fine radiating strize and with a decol- 
lated apex, as usual in fresh water shells. Another small, capuloid species has 
been found in the brackish water at Port Canning; it is as yet undescribed. 
Messrs. Adams divide the family into four genera (excluding Lepeta), namely— 
1. Helcion, Montfort, 1810. 
1. a. sub-genus Sevtellina, Gray, 1847. 
2. Nacella, Schumacher, 1817 (H. and A. Adams’ Gen. I, p. 467). 
3. Scurria, Gray, 1847. 
4. ‘Tectura, Audouin and M. Edw., 1880 (demea, Eschholtz, Patelloidea, 
Quoy and Gaimard). 
Gray places Helcion in the Parzizipa, but says that the gills are interrupted 
over the head, consisting of filiform strands. The form of the latter is very 
nearly the same as in other Zzcrverpa#, and if the teeth do not differ, it would 
probably be better to retain the genus in this family. Gray also pronounces the 
genus Scuwtellina to be identical with Helcion, from which the shells are not 
