1376 i'i.i:ii)i)(iN 



inner united to the abdominal sac; genitalia ocupying- each 

 side the lateral part of the visceral mass as far forward as the 

 foot; mantle closed below the branchial siphon, and united 

 into branchial and anal sii)hons ; anal opening rather small ; 

 branchial large, separated by a solid bridge, which solders to- 

 gether the extremities of the four branchire ; both orifices have 

 a thickened inner edge ; the branchial being furnished with 

 short tubercles or granules : mantle united below posteriorly 

 one- fourth its length: foot large and strong; adductor mus- 

 cles strong. (Pelseneer.) 



Type, Iridina ovata Swainson. 



In this small group the taxodont teeth, which are more or 

 less characteristic of the Mutelid?e, are strongly developed. I 

 have used the name Camcronia of Hourguignat in a subgeneric 

 sense. 



Subgenus Pleiodon s. s. 



Characters as in the genus. 



Pr.EiODON ovATus (Swainson). 



Shell generally irregularly obovate, subinflated, solid, slight- 

 ly inequilateral ; beaks full and high ; posterior ridge rounded, 

 ending in a rounded point about on the median line, above it 

 there is a radial, shallow excavation or furrow, which some- 

 times ends in a light sinus at the obliquely truncate margin of 

 the dorsal slope ; dorsal outline lightly arched, anterior end a 

 little narrowed, rounded, often subangulate above; base line 

 curved, fullest behind the middle ; surface nearly smooth, con- 

 centrically striate and having indications of radial sculpture ; 

 epidermis dark olive-green, lighter at the beaks; hinge with 

 numerous, irregular, taxodont teeth, the anterior ones oblique, 

 the posterior ones somewhat V-shaped ; dorsal scars forming 

 irregular rows running from the beaks towards the anterior 

 base ; muscle scars lightly impressed ; nacre whitish to pale 

 violet, sometimes greenish often brilliantly iridescent. 



Length 114, height 64, diam. 37 mm. 



Length 105, height 64, diam. 42 mm. 



West Africa. 



