﻿512 MAKCAUITANA 



not closed below ; iiiarsupium ocoup}ing- the entire (juter gills. 

 iMjot and abdomen small ; whole animal dark colored. 



Type. M ya iiiari:;aritifrra Ijnnanis. 



A honiogeneons G;-ron]) having a circumboreal distribution 

 with two species in the warmer temperate region of the United 

 States and one, singularly isolated, in the Oriental Tropics. 

 Most of the species have shells with defective hinge teeth and 

 in none of them are they very strongly developed. All have 

 simple, more or less arcuate, shells with dull colored, thick, 

 dark epidermis, and 'gills that are free from the mantle at the 

 posterior end. I have examined a great many animals of the 

 Margaritana mar gar it if era taken at different seasons and in 

 many localities but have never found one gravid. Von VVahl 

 states that the marsupium occupies the entire outer gills, and 

 I have been informed that specimens have been found with a 

 few embryos in the inner gills also. 



The name Baphice Meuschen has precedence, but was never 

 described ; it was applied to a miscellaneous lot of bivalves, 

 and is in the plural number. Retzius's first species in Unio, 

 the type of a section without laterals, is the IJ. margaritifer, 

 but in 17()2 l>ruguiere in Choix de Memoires, 1, p. 106, fully 

 and carefully redefmcd the genus Unio, restricting it to species 

 with cardinal and lateral teeth. 



Ortmann. ( Xaut. XX\'. 191 r, p. 6). separates this genus 

 from the Unionidcc and proposes the family Margaritanidcc 

 for its reception. "The chief differences of this family are 

 found in the inconnplete gill-(lia])hragm ; in the entire lack of 

 a tendency to ai)i)roach or to luiite the mantle margins to 

 form siphons ; in the structure of the gills, which lack regular 

 septa running parallel to the gill-hlaments, and, consequently, 

 in the lack of the well-defined water-tubes (ovisacs in the 

 female) : in the marsu])ium being formed by all four gills ; 

 and in the small size and globular shape of the glochidium. 

 without true hooks." P.ut Lefevre and Curtis, (Bull. Bur. 

 Fish.. XXX, 1912, p. tt8). consider this "a procedure of 

 /doubtful wisdom." 



