36 NOMENCLATURE. 



or membranaceous substance, and varies 

 much in shape and contexture. 



Radii. Rays: elevated striae tending from the 

 centre to the periphery. 



Rostrum. Beak, formed by both lips being 

 produced towards the base into an atte- 

 nuated or narrow process. 



SiPHO or SiPHUNCULUS. Siphon : a small cy- 

 lindrical canal perforating the partition in 

 a chambered shell, is either centralis, 

 through the centre ; lateralis, through the 

 margins of the partitions ; or olliquus, 

 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. 



