24 



SYSTEMATIC ARRANGEMENT 



a. Volutina. Siphon with auricles on sides of base. Tentacles far 

 apart, united by a broad veil forming a hood over the head. 

 Eyes far back, behind the small tentacles. 



f Teeth broad, lunate ; apex three-lobed (fig. 17). 



a. Yetina. Animal viviparous ; nucleus of shell very large, irre- 

 gular, callous (fig. 18). Foot very large. Operculum none. 



I. Yetus. 



Shell ventricose, covered with a horny peri- 

 ostraca, more or less covered with a polished 

 shelly coat deposited by the expanded mantle ; 

 spire very short, irregular ; mouth expanded. 

 Animal large, ovoviviparous ; the young very 

 large when born. Foot very large, partly 

 covering the shell. Operculum none. 



Fig. 17.— Yetus olla. 



* Left side of mantle and inner lip rather expanded, 

 suture of adult broadly channeled. 



1. Y. Navicula. Spire short. 



2. Y. Cymbium. Spire subconic. 



3. Y. gracilis. Spire produced. 



Shell mottled ; 



** Left side of mantle and inner lip much expanded over the last 

 whorl. Shell one-coloured. 



4. Y. Neptuni, t. 25. f. 2 ; Kiener, t. 88. f. 3, 



t. 27. f. 4 ; Adams, Gen. Moll. t. 1 . f. 3. 

 Var. Y. patula and Y. Tritonis. Suture 

 channel wide. 



5. Y. olla. Suture channel narrow, deep. 



Fig. 18. 



Young Y. proboscidalis 



*** Left side of mantle and inner lip covering 

 the whole outer surface of the shell. 



6. Y. proboscidalis. 



7. Y. porcina. 



8. Y. rubiginosa. 



The original surface, indicating the extension of 

 the mantle over the surface of the shell in this 

 and other genera of this family, is often destroyed 

 in cabinet specimens, even in the most recently- 

 formed collections, which greatly deteriorates from 

 their scientific value. 



