312 THE PEARLY FRESH-WATEE MUSSELS— SIMPSON. vol. xvm. 



l^art of tlie valves a little way apart, and this probably prevents tlie 

 teeth from coming in contact. A single dorsal scar can be made out on 

 the inner part of each hinge plate in front of the beaks; the posterior 

 muscle scars are united, as are the anterior ones, and the palleal line 

 is distinct. Nothing is known of the soft parts of this mollusk, but it 

 probably belongs to the Unionid;e, as the teeth, nacre, and muscle scars 

 agree with those of that family. IJnio languilati, Heude, may be con- 

 sidered the type of the genus. 



Genus CRISTARIA, Schumacher. 



In ISl-t Leach ^ bestowed the generic name Dipsas on Anodonta plicata 

 (Humphrey), Solander. This name had been used by Laurin 17C8, and 

 for that reason could not stand. Barhula, frequently applied to this 

 and allied species, is an anonymous catalogue name, attributed to 

 Humphrey. Cristaria, bestowed by Schumacher in 1817, ^ will have to 

 be applied to the group. It consists of a few species of large, thin, 

 usually more or less symphynote Kaiades, inhabiting Chinese and Jap- 

 anese Avaters. Usually there is, especially in younger shells, a fair 

 development of lateral teeth, which, however, are often entirely wanting 

 in old specimens, and occasionally there are rudimentary lamellar cardi-. 

 nals. Some of the species have a row of peculiar, small corrugations or 

 plications running from the beaks to the outer edge of the dorsal slope. 



I know nothing of the anatomy of this genus,^ but from a careful 

 comparison of the shells of several of the species with those of various 

 Chinese Unios, I think it probable that they are depaui)erate forms, 

 "which have descended from the group typified by U. cumingi., Lea. 

 This species often shows plainly a row of plications on the dorsal slope, 

 as do G.pUcatus and C. spatiosa. In the Unios of the Cumingi group tlie 

 cardinals are often more or less blurred, or nearly wanting in such 

 sj)ecies as TJ. delaporti, Crosse and Fischer, U. myersianiis, Lea, and V. 

 delphinns^ Lea. Their teeth are sometimes broken up into small denticles 

 or nodules, after the manner of those of certain Hyrias. The sui)pres- 

 sion of the teeth in the Cristarias is probably caused by the fact that 

 they are inhabitants of muddy places and still water, and they do not 

 therefore need teeth, as do the Unios which iuliabit streams. ]Maiiy of 

 these are abundant in the rice fields of China and Japan. As the group 

 seems to be a tolerably natural one, it perhaps may stand as a genus. 

 Unio swinhoi, A<lams, of which a shell in the National Museum collection 

 (Xo. 850G9) is said to have come from Formosa, is a thin, somewhat 

 inflated shell, with greatly compressed, feeble cardinals and laterals, 

 and the specimen examined seems very near to Cristaria discoidea, Lea, 



iZool. MiscelL, I, p. 119, 1814. 



^Essai d'un nouv. syst., p. 107, 1817. 



^Tlie auatiOuiy of the species Cristaria plicata lias been woikert up, I believe, tinder 

 the title of Dipsas plicata, Lea, l>y Islikewara in his "Introduction to the Anatomy 

 of Animals," published in .Fapanese at Tokio. The paper is not accessible to me. 



