330 PHOLADDLE. 



embedded in the interior of madrepores and fragments of 

 calcareous rocks, already comprises four recent species. 



Species of Jouannetia. 



Cumingii, Sow. globosa, Quoy and Gaim. 



Darwinii, Sow. pectiuata, Conr. 



Genus PARAPHOLAS, Conrad. 



Siphons naked. 



Shell ovate-oblong, the front gape at length closed by a 

 callous plate ; valves equal, with two oblique sulci extending 

 from the beaks to the base, with longitudinal laminae 

 between them ; dorsal valves two. 



Ex. P. quadrizonalis, Spengler, pi. 90, fig. 4, 4, a. 



These shells may be known by the two oblique grooves 

 which divide the surface of the valves, and by the two dorsal 

 plates. 



Species of Parapholas. 



concamerata, Desk. ovoidea, Gould. 



Janellii, Desk. quadrizonalis, Spengl. 



Genus MARTESIA, Leach. 



Siphons naked. 



Shell ovate-oblong, the front gape at length closed by 

 a callous plate ; valves equal, regularly divided in front by 

 a furrow extending from the beaks to the base ; dorsal valve 

 single, lanceolate or peltate. 



Syti. Penitella, Conrad. 



Ex. M. striata, Linnaeus, pi. 90, fig. 5, 5, a. 



