1918.] B. Prashad : The Anatomy of Indian Mollusca, 



145 



development took place. In the other variety ohesa (H. and T.) also 

 only the outer pair of gills serve as the marsupium. I have found by a 

 study of sections of the gills of males, gravid and sterile females that the 

 differences in the structure of the respiratory and marsupial gills, origin- 

 ally described by Peck^ for the gills of Anodonta and later on found by 

 Ortmann'- to be constant in a large number of other genera as well, are 

 the same in Lamellidens and Parreyssia, and so need not be detailed here. 

 In the marsupial gills the inter-lamellar junctions are more numerous 

 than in the respiratory gills, the epithelial covering of the lamellar 

 junctions is modified ; whereas in the purely respiratory gills of the 

 female and those of the male the inter-lamellar junctions are fewer and 

 the epithelial covering is of the ordinary type. As expected by Ortmann 

 the gills do not swell very much when full of glochidia and their lower 

 margins are always sharp and distended. In the firsc variety no glo- 

 chidia were found but the embryos were found to be agglutinated 

 together to form a flat more or less elliptic plate, thick and broad above, 

 thin and tapering below. 



The glochidia of the second variety obesa (H. and T.) may be de- 

 scribed as semi-elliptic (fig. la) with a rounded ventral margin, the hinge- 

 line rather long and nearly straight and measuring -248 mm. by -210 mm. 



Parreyssia. 



The number of species and varieties of this genus which was studied 

 was much larger than of the others. In the following table I give the 

 locality, date on which collected, the gills in which the glochidia were 

 found and the size of the glochidia. It is of interest to note that the 

 specimens were from such widely separate localities as Eastern Bengal, 

 Chota Nagpur and the Western Ghats in the Bombay Presidency. One 

 of the forms which I have marked with a query seems to be either an 

 undescribed variety of P. favidens, or possibly a distinct species. 



1 Q. J. Microsc. Sci. XVII, pp. 43-66 (1877). 



2 Mem. Carnegie Mus. IV, pp. 279-347, pis. Ixxxvi-lxxxix (1911). 



E 2 



