316 THE PEARLY FRESH-WATEB MUSSELS— SIMPSON. vouxvni. 



the fact that authors generally have based this genus on F. iruncatus, 

 it must be established on P. ohUquns, the first-described species.^ 



The corrugated species of this genus have somewhat radiately sculp- 

 tured beaks, while the smooth forms seem to be destitute of beak 

 sculpture. 



Genus SOLENAIA, Conrad.= 



In southeastern Asia and possibly Australia there is a group of 

 remarkable fresh-water bivahes, having a greatly elongated shell and 

 foot, and bearing some resemblance to Mycetopiis of South America. 

 Lea placed these forms with this genus,^ but in 18G9 Conrad called 

 attention to the fact that the shells had a long rudimentary lateral, 

 and gave them a generic name, as above. Fischer, in a carefully written 

 paper,* places the oriental forms in Mycetopus. The foot of the latter 

 genus is enormously developed, cylindrical, and enlarged at its 

 extremity like a mushroom. This remarkable configuration of the 

 shell and foot are to enable the animal to burrow in the sand or mud, 

 where it lives in a vertical position. Fischer communicated with 

 Heude in China, who had described a large number of species, and at 

 his request the latter gathered all the information possible concerning 

 the s])ecies of that country. They, too, have a greatly elongated foot, 

 enlarged into a button at its extremity, and burrow in the mud in 

 shallow water. Fischer was no doubt deceived by the fact that similar 

 environment had i^roduced similar modifications in two unrelated 

 groups. Unio dehiscens, Say, of the United States, has an elongated 

 shell and a greatly lengthened club-shaped foot, and it also burrows; 

 and I have mentioned the case oi Anodonta angulata^ Lea, which buries 

 itself in the bottoms of rivers and closely resembles one of Heude's 

 species. Unio anodontoides, Lea, a well-known form of the Mississippi 

 Valley, was found by Mr. John B. Henderson, jr., in burrows from nine 

 to twelve inches deep, in soft mud in the Maramec Eiver, Missouri, with 

 the foot greatly distended. Yet none of these are Myceiopus., or at all 

 closely related to it. 



The South American species difier considerably in form from those 

 of Asia, being generally more rounded i)<>steriorly, their shells smooth 

 and of a delicate texture, and having interiorly a wonderfulh' soft, 

 pearly nacre, while the oriental forms are rather rough, often concen- 

 trically sculptured, and covered with a heavy epidermis; the nacre, 



'Lea applied Schumacher's name Priso^ow to the P. truncatus of that author (Syn- 

 opsis of the UnionidiP, p. 27, 1870), stating that this name {I'risodon) could not be 

 used for his first species (P. obliquiis) because Klein, in 1753, had given the name 

 Triquetra to these symphynote Naiades. As Klein was not a binomial author, Tri- 

 quetra can not stand, and the generic name Prisodon will have to be given to /'. obli- 

 qitus and the species of that group. Schumacher's Paxyodon, described on page 139 

 of the Essai, is also a Prisodon. 



2Amer. Journ, Conch., IV, pt. 4, p. 249, 1869. 



'Synopsis of the Unionida', p. 90. 



"* Journ. de Conch., XXXVIII, p. 93, 1890. (Observations on the genera Mycetopus 

 And SoJenaia. Second note.) 



