STUDIES ON THE ANATOMY OF INDIAN 

 MOLLUSCA. 



1. THE MARSUPIUM AND GLOCHIDIUM OF THE 

 GENUS PHY SUN 10. 



By Baini Puashad, M.Sc, Superintendent of Fisheries, 

 Bengal Fisheries Laboratory , Indian Museum, Calcutta. 



(Plate XXII). 



On the occasion of a tour in the Southern Shan States Dr. N. Annan- 

 dale and Dr. F. H. Gravely collected specimens of two new species of 

 the genus Physunio, Simpson. These are the only two Unionidae found 

 in the basin of the Inle Lake, where the specimens were collected. P. 

 ferrugineus: is a true lacustrine form and is found in the middle of the 

 lake in very clear water, whilst the other species (P. microfteroides) is 

 found in a muddy stream opening into the lake. 



Dr. Annandale was kind enough to give me specimens of both the 

 forms in order that I might describe their glochidia. Whilst working 

 out the structure of these, it was found that the marsupium of the genus 

 was peculiar, and an account of this structure is also included here. 

 At Dr. Annandale's suggestion I looked through the large collection of 

 fishes made at the same locality, and I was fortunate enough to find 

 specimens with glochidia attached to their fins. 



My sincere thanks are due to Dr. Annandale for giving me the oppor- 

 tunity of making this very interesting study, and for kind help at all 

 times. I am also highly obliged to Mr. T. Southwell, A.R.C.S., F.Z.S., 

 Director of Fisheries, Bengal and Bihar and Orissa, for kindly allowing 

 me to undertake and publish this work. 



Marsupium. — By the term marsupium in the description of the 

 freshwater mussels, we mean those portions of the gills in which the eggs 

 are received from the supra-branchial chambers after ovulation and 

 which serve as brood-pouches for the retention and nurture of the 

 embryos and glochidia until the latter are shed. As different portions of 

 the gills are specialized in the various groups of Unionidae to serve as 

 a marsupium and as this has been found to be a constant character, the 

 marsupium has been used as the chief diagnostic character of these 

 groups. Simpson (4) divided the Unionidae according to this character 

 into Exobranchiae, with the marsupium comprising the outer gill on 

 each side or all four gills, and the Endobranchiae, in which the inner pair 

 of gills alone serve as the brood-pouch. In the genus Physunio nothing 

 was known about the anatomy of the animal, but Simpson, judging from 

 the shell-characters alone, was led to include it amongst the Endo- 

 branchiae. This was an entirely wrong conclusion. Gravid females 

 were found in both the two new species collected and described by 

 Dr. Annandale, aud it is to this fortunate chance that I owe the descript- 

 ion of the marsupium and the glochidium of the genus. No attempt 

 is made to describe the histological or anatomical structure of the gills 

 in the present account as the anatomy of the animal is being described 

 in detail by Dr. Ekendranath Ghosh. 



