20 
NOMENCLATURE. 
or membranaceous substance, and varies 
much in shape and contexture. 
Radii. Rays; elevated strise tending from the 
centre to the periphery. 
Rostrum. Beak, formed by both lips being 
produced towards the base into an attenu- 
ated or narrow process. 
SiPHo seu SiPHUNCULus. Siphon ; a small 
cylindrical canal perforating the partition 
in a chambered shell, is either centralis, 
through the centre ; lateralis, through the 
margins of the partitions ; or obliquus, 
cutting the axis of the whorls. 
Spira. Spire; the upper whorls collectively. 
cariosa. Carious ; corroded, or, as it were, worm- 
eaten. ' 
capitata. Capitate ; terminated by an obtuse 
head. 
exquisita. Exserted ; much attenuated. 
plana. Flat ; having the upper whorls of an equal 
height, so that the spire appears truncate. 
retusa. Retuse; having the lower whorls of the 
spire pressed into the body. 
