380 Terebratulanina. MOLLUSCA.- Discinid^. 
Tribe II. — MAGASINA. 
Tribe I.— TEREBRATULANINA. ■ 
In this tribe the species have the shelly loop at- 
The species belonging to this tribe have the shelly 
tached to the septum, in the middle of the dorsal 
loop attached to the hinge plate, and is composed of 
valve, and is composed of six recent genera — Tere- 
three genera, Terehratula, Terebraiulina, and Wald- 
hratella, Magas, Bouchnrdia, Megerlia, MorHsia, and 
lieimia. 
Kraussia. 
Order II.— CEYPTOBRACHIA. 
Family— THECIDEID^. 
Gen'US Argiope.— This genus has the loop folded 
into two or four lobes, and adhering to the prominent 
This is the only family of recent shells contained in 
septa with which the dorsal valve is furnished in- 
the order. The animals have the oral arms folded 
teriorly. 
upon themselves, united by membrane, fringed with 
Genus Thecidea. — This genus has an unsymme- 
long cirrhi on their outer margins, and supported by a 
trical loop divided into two or more lobes which are 
shelly loop. The mantle extends to the margin of the 
united more or less intimately with grooves formed in ' 
valves, and adheres closely. 
the disc for t-heir reception. 
Sub-class IL— HELICTOPODA. 
This sub-class consists, like the preceding, of two 
band arising from the hinder or cardinal edge of the 
orders — the Sclerobrachia and the Sarcobrachia, 
ventral valve ; the second, having the oral arms fleshy 
the first having the oral arms, supported by a shelly 
to the base, and without any shelly support. 
Order I.— SCLEROBRACHIA. 
In this order there is only one family of recent shells. 
Genus Rhynchonella. — T his genus has a trigonal 
and this consists of a single genus. 
shell, usually plaited, and acutely beaked. Externally it 
is not punctate, and internally it has no testaceous skele- 
Family— RHYNCHONELLID AH. 
ton or apophysar}" system. The dorsal valve is elevated 
in front, and depressed at the sides, whilst the ventral 
The Rhynchonellas have elongate, fleshy, spiral, oral 
valve is hollowed along the centre. The foramen is 
arms, supported at the base by two short, hard, diverg- 
triangular and open, situate under the beak. Only 
ing shell-laminse arising from the hinge margin of the 
two recent species are known ; one from the northern 
ventral valve. 
seas, and the other from New Zealand. 
Order II.— SARCOBRACHIA. 
This order is composed of three families of recent 
Great Britain, the Mediterranean, India, and New 
shells, all distinguished by there being no processes on 
South Wales. 
the hinge-margin or disc in the lower valve, though in 
some of them there is a slight medial longitudinal 
Family^DISCINIDAI:. 
elongation. 
The Discinas, like the preceding family, have the 
oral arms fixed to a process of the ventral valve : but 
Family — CRANIIDAH. 
the shell is horny, and when fresh and moist, is quite 
flexible, and is attached to marine bodies by a short ten- 
The Cranias have the oral arms fixed to a process 
dinous peduncle, which passes through a small slit in 
of the ventral valve. The shell of Crania is. orbicular. 
the disc of the lower valve. The upper valve of Dis- 
calcareous ; the dorsal or upper valve of a conical 
cina is conical, and resembles the shell of a limpet or 
form, and the lower or ventral valve entire, flat, and 
patella, the lower is orbicular and flat ; they are not 
attached by its outer surface to marine bodies. Five 
united together by a hinge, and the external surface is 
recent and twenty-eight fossil species are known. The 
minutely punctate. Seven recent species are known, 
recent ones are natives of the north seas, the coasts of 
chiefly from South America. 
