106 THE NAUTILUS. 



The larvae of JJnio and Quadrula are glochidia of simple, semi- 

 circular or semi-elliptical outline, with the anterior and posterior end 

 practically undistinguishable in the shell. 



Asiatic Forms. 



Parreysia wynegungaensis (Lea) (see Nautilus, April, '10, pi. VI, 

 fig. 4, and pi. VII, fig. 3) has essentially the structure of Quadrula. 

 The anal and branchial openings, the diaphragm, the palpi, gills and 

 marsupium are practically identical, as is also the general shape and 

 insertion of the gills (the inner separated from the posterior end of 

 the palpi). The only differences are found in the separation of the 

 anal and supraanal, which is somewhat longer, in the attachment of 

 the inner lamina of the inner gills to the abdominal sac, and in shell 

 characters, chief of which is the "radial sculpture." 



In addition I have investigated a species of Lamellidens, to which 

 I am also indebted to the courtesy of Mr. Frierson. 



Lamellidens consohrinus (Lea) from India; a sterile female is at 

 hand. This is generally like Parreysia in structure, not only in 

 those characters which agree with Quadrula, but also in the supra- 

 anal, which is rather widely separated from the anal, and in the 

 inner lamina of the inner gills, which is connected with the abdominal 

 sac. 



But there is an important exception; only the outer gill is marsu- 

 pial, and at the posterior end of this gill there is almost one-fourth 

 of it of non-marsupial structure. 



The septa are of the Quadrula and Unio type, but in the marsu- 

 pial part of the outer gill I observe some septa which are not com- 

 plete (see pi. VII, fig. 4), i. e., they arise from either lamina without 

 meeting in the middle of the interlaminar space; other septa are 

 connected only by their epithelial tissue, but most of them are 

 complete. 



Possessing only a single individual, it is impossible to decide 

 whether this is a permanent or temporary structure. It might be 

 that the incomplete septa of the sterile female becomes complete in 

 the gravid female. 



In a general way Lamellidens has the same relation to Parreysia 

 as Unio has to Quadrula. But it is by no means identical with Unio : 

 the structure of the supraanal, the inner lamina of the inner gill and 

 the marsupium separates it sufficiently. It remains to be seen 

 whether the posterior part of the outer gill is always non-marsupial. 



