II04 PARREYSIA 



closely related to Nodularia. Roth groups, as I have constitut- 

 ed them, have numerous representatives in Tropical Africa 

 and southeast Asia. The shells of this group are generally- 

 more solid, more inflated and shorter than those of Nodularia. 

 The beaks and earlier growth, as a rule are rather more strong- 

 ly sculptured with zigzag-radial ridges than are those of that 

 genus and the pseudocardinals are heavier and more split up. 

 In a great many species there are small tubercles on the hinge 

 plate, behind the pseudocardinals. The beak cavities are, as a 

 rule, deeper than those of the species of Nodularia. 



Ortmann, (1. c), from an examination of P. wynegungcen- 

 sis Lea, remarks : "Soft parts partly primitive, partly more 

 advanced. Super-anal separated from the anal by a well-de- 

 veloped mantle-connection, which is rather long. Inner lam- 

 ina of inner gills entirely connected with the abdominal sac. 

 All four gills are marsupial in the female, with well-developed 

 septa and water-tubes, which latter are somewhat narrower in 

 the outer gill than in the inner. In the male, the septa are dis- 

 tinctly more distant than in the female. During pregnancy, 

 the gills swell but little, and the edges remain sharp, and the 

 ovisacs remain simple. Placentae subcylindrical, only slightly 

 compressed, and not very solid. Glochidia not observed." 



Kf,y to the groups of Parreysia. 



Shell with imperfect laterals. Group of P. biesiana. 



Shell generally having perfect laterals. 

 Ovate, obovate or elliptical. 



Small, ovate with strong, concentric outer ridges. 



Group of P. aurora. 

 Medium sized ; beaks high, strongly sculptured ; 

 pseudocardinals strong and ragged. 



Group of P. corrugata. 

 With a high, pinched-up posterior ridge. 



Group of P. chinensis. 

 Beak sculpture very strong, extending part way over 

 the disk, abruptly changing to concentric sculpture. 



Group of P. bakeri. 



